Wafer-level hermetic micro-device packages

ABSTRACT

A method for manufacturing a hermetically sealed micro-device package encapsulating a micro-device. The package includes a transparent window allowing light to pass into and out of a cavity containing the micro-device. A first frame-attachment area is prepared on semiconductor substrate having a micro-device operably disposed thereupon, the first frame-attachment area having a plan that circumscribes the micro-device. A second frame-attachment area is prepared on a sheet of transparent material, the second frame-attachment area having a plan that circumscribes a window aperture portion of the sheet. A frame/spacer is positioned between the semiconductor substrate and the sheet, the frame/spacer including a continuous sidewall having a plan on one side substantially corresponding to, and substantially in register with, the plan of the first frame-attachment area, having a plan on the opposite side substantially corresponding to, and substantially in register with, the plan of the second frame-attachment area, and having a height that exceeds the height of the micro-device. Next the substrate, frame/spacer and window are bonded together to form a hermetically sealed package encapsulating the micro-device in a cavity below the window aperture portion of the transparent sheet.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.10/713,475 filed Nov. 14, 2003, now U.S. Pat. No. 6,962,834, which is aContinuation-In-Part of U.S. patent application Ser. No. 10/133,049filed Apr. 26, 2002, now U.S. Pat. No. 6,723,379, which is aContinuation-In-Part of U.S. patent application Ser. No. 10/104,315filed Mar. 22, 2002, now U.S. Pat. No. 6,627,814. U.S. Pat. No.6,962,834 also claims benefit of U.S. Provisional Application60/426,522, filed Nov. 15, 2002, from U.S. Provisional Application60/442,922, filed Jan. 27, 2003, and from U.S. Provisional Application60/442,941, filed Jan. 27, 2003. The following co-pending applicationsalso claim the benefit of U.S. Pat. No. 6,962,834: U.S. patentapplication Ser. No. 10/766,493 filed Jan. 27, 2004 and U.S. patentapplication Ser. No. 11/140,593 filed May 27, 2005.

TECHNICAL FIELD OF THE INVENTION

The current invention relates to packages for photonic devices, opticaldevices, micro-mechanical devices, micro-electromechanical systems(MEMS) devices or micro-optoelectromechanical systems (MOEMS) devices,and more particularly, to manufacturing hermetic packages having atransparent window at the wafer level or substrate level of devicefabrication.

BACKGROUND OF THE INVENTION

Photonic, photovoltaic, optical and micro-mechanical devices aretypically packaged such that the active elements (i.e., the emitters,receivers, micro-mirrors, etc.) are disposed within a sealed chamber toprotect them from handling and other environmental hazards. In manycases, it is preferred that the chamber be hermetically sealed toprevent the influx, egress or exchange of gasses between the chamber andthe environment. Of course, a window must be provided to allow light orother electromagnetic energy of the desired wavelength to enter and/orleave the package. In some cases, the window will be visiblytransparent, e.g. if visible light is involved, but in other cases thewindow may be visibly opaque while still being “optically” transparentto electromagnetic energy of the desired wavelengths. In many cases, thewindow is given certain optical properties to enhance the performance ofthe device. For example, a glass window may be ground and polished toachieve certain curve or flatness specifications in order to disperse ina particular pattern and/or avoid distorting the light passingtherethrough. In other cases, anti-reflective or anti-refractivecoatings may be applied to the window to improve light transmissiontherethrough.

Hermetically sealed micro-device packages with windows have heretoforetypically been produced using cover assemblies with metal frames andglass window panes. To achieve the required hermetic seal, the glasswindow pane (or other transparent window material) has heretofore beenfused to its metallic frame by one of several methods. A first of thesemethods is heating it in a furnace at a temperature exceeding thewindow's glass transition temperature, T_(G) and/or the window'ssoftening temperature T_(S) (typically at or above 900° C.). However,because the fusing temperature is above T_(G) or T_(S), the originalsurface finish of the glass pane is typically ruined, making itnecessary to finish or re-finish (e.g., grinding and polishing) bothsurfaces of the window pane after fusing in order to obtain thenecessary optical characteristics. This polishing of the window panesrequires additional process steps during manufacture of the coverassemblies, which steps tend to be relatively time and labor intensive,thus adding significantly to the cost of the cover assembly, and henceto the cost of the overall package. In addition, the need to polish bothsides of the glass after fusing requires the glass to project both aboveand below the attached frame. This restricts the design options for thecover assembly with respect to glass thickness, dimensions, etc., whichcan also result in increased material costs.

A second method to hermetically attach a transparent window to a frameis to solder the two items together using a separate preform made of ametal or metal-alloy solder material. The solder preform is placedbetween a pre-metallized window and a metal or metallized frame, and thesoldering is performed in a furnace. During soldering, no significantpressure is applied, i.e., the parts are held together with only enoughforce to keep them in place. For this type of soldering, the most commonsolder preform material is eutectic gold-tin.

Eutectic gold-tin solder melts and solidifies at 280° C. Its CTE at 20°is 16 ppm/° C. These two characteristics cause three drawbacks to thereliability of the assembled window. First, the CTE of Mil-Spec Kovarfrom 280° C. to ambient is approximately 5.15+/−0.2 ppm/° C., while mostwindow glasses intended for sealing to Kovar have higher average CTEsover the same temperature range. During cooling from the set point of280° down to ambient, the glass is shrinking at a greater rate than theKovar frame it is attached to. The cooled glass will be in tension,which is why it is prone to cracking. To avoid cracking, the glassshould have an identical or slightly lower average CTE than the Kovar soas to be stress neutral or in slight compression after cooling. Usingsolders with lower liquidus/solidus temperatures puts the Kovar at ahigher average CTE, more closely matching the average CTE of the glass.However, this worsens the second drawback of metal-allow solder seals.

The second drawback to soldering the glass to the Kovar frame is thatthe window assembly will delaminate at temperatures above the liquidustemperature of the employed solder. Using lower liquidus/solidustemperature solders, while reducing the CTE mismatch between the Kovarand glass, further limits the applications for the window assembly. Mostlead-free solders have higher liquidus/solidus temperatures than the183° C. of eutectic Sn/Pb. Surface-Mount Technology (SMT) reflow ovensare profiled to heat Printed-Wiring Board (PWB) assemblies 15-20 degreesabove the solder's liquidus/solidus temperature. Thus, the SMTreflow-soldering attachment to a PWB of a MOEMS device whose window wasmanufactured using lower melting-point solder preforms might have theunfortunate effect of reflowing the window assembly's solder, causingwindow delamination.

The third drawback is that the solder, which is the intermediate layerbetween the glass and the Kovar frame, has a CTE up to three timesgreater than the two materials it is joining. An intermediate joiningmaterial would ideally have a compensating CTE in-between the twomaterials it's bonding.

A third method to hermetically attach a glass window to a frame is tosolder the two items together using a solder-glass material.Solder-glasses are special glasses with a particularly low softeningpoint. They are used to join glass to other glasses, ceramics, or metalswithout thermally damaging the materials to be joined. Soldering iscarried out in the viscosity range h where h is the range from 10⁴ to10⁶ dPa s (poise) for the solder-glass; this corresponds generally to atemperature range T (for the glass solder or solder-glass) within therange from 350° C. to 700° C.

Once a cover assembly with a hermetically sealed window is prepared, itis typically seam welded to the device base (i.e., substrate) in orderto produce the finished hermetically sealed package. Seam welding uses aprecisely applied AC current to produce localized temperatures of about1,100° C. at the frame/base junction, thereby welding the metallic coverassembly to the package base and forming a hermetic seal. To preventdistortion of the glass windowpane or package, the metal frame of thecover assembly should be fabricated from metal or metal alloy having aCTE (i.e., coefficient of thermal expansion) that is similar to that ofthe transparent window material and to the CTE of the package base.

While the methods described above have heretofore produced useablewindow assemblies for hermetically sealed micro-device packages, therelatively high cost of these window assemblies is a significantobstacle to their widespread application. A need therefore exists, forpackage and component designs and assembly methods that reduce the laborcosts associated with producing each package.

A need still further exists for package and component designs andassembly methods that will minimize the manufacturing cycle timerequired to produce a completed package.

A need still further exists for package and component designs andassembly methods that reduce the number of process steps required forthe production of each package. It will be appreciated that reducing thenumber of process steps will reduce the overhead/floor space required inthe production facility, the amount of capital equipment necessary formanufacturing, and handling costs associated with transferring the workpieces between various steps in the process. A reduction in the cost oflabor may also result. Such reductions would, of course, further reducethe cost of producing these hermetic packages.

A need still further exists for package and component designs andassembly methods that will reduce the overall materials costs associatedwith each package, either by reducing the initial material cost, byreducing the amount of wastage or loss during production, or both.

SUMMARY OF THE INVENTION

The present invention disclosed and claimed herein comprises, in oneaspect thereof, a method for manufacturing a hermetically sealedmicro-device package encapsulating a micro-device. The package includesa transparent window allowing light to pass into and out of a cavitycontaining the micro-device. A first frame-attachment area is preparedon semiconductor substrate having a micro-device operably disposedthereupon, the first frame-attachment area having a plan thatcircumscribes the micro-device. A second frame-attachment area isprepared on a sheet of transparent material, the second frame-attachmentarea having a plan that circumscribes a window aperture portion of thesheet. Next, a frame/spacer is positioned between the semiconductorsubstrate and the sheet, the frame/spacer including a continuoussidewall having a plan on one side substantially corresponding to, andsubstantially in register with, the plan of the first frame-attachmentarea, having a plan on the opposite side substantially corresponding to,and substantially in register with, the plan of the secondframe-attachment area, and having a height that exceeds the height ofthe micro-device. Next the substrate, frame/spacer and window are bondedtogether to form a hermetically sealed package encapsulating themicro-device in a cavity below the window aperture portion of the windowsheet.

The present invention disclosed and claimed herein comprises, in anotheraspect thereof, a hermetically sealed micro-device package encapsulatinga micro-device. The package includes a transparent window allowing lightto pass into and out of a cavity containing the micro-device. Themicro-device package comprises a semiconductor substrate, a sheet oftransparent material and a frame/spacer. The semiconductor substrate hasa micro-device operably disposed thereupon, and also a firstframe-attachment area is formed thereupon having a plan thatcircumscribes the micro-device. The sheet of transparent material has awindow aperture portion defined thereupon, and also has a secondframe-attachment area formed thereupon having a plan that circumscribesthe window aperture portion. The frame/spacer is positioned between, andhermetically bonded to, the semiconductor substrate and the transparentsheet. The frame/spacer includes a continuous sidewall having a plan onone side substantially corresponding to, and substantially in registerwith, the plan of the first frame-attachment area, a plan on theopposite side substantially corresponding to, and substantially inregister with, the plan of the second frame-attachment area, and aheight that exceeds the height of the micro-device.

The present invention disclosed and claimed herein comprises, in yetanother aspect thereof, a method for manufacturing multiple hermeticallysealed micro-device packages simultaneously. Each package willencapsulate a micro-device and include a transparent window apertureallowing light to pass into and out of a cavity containing themicro-device. On a unitary semiconductor substrate having a plurality ofmicro-devices operably disposed thereupon, a first frame-attachment areais prepared having a plan that circumscribes each of the micro-devices.On a unitary sheet of transparent material, a second frame-attachmentarea is prepared having a plan that circumscribes a plurality oftransparent window aperture portions of the sheet. A frame/spacerincluding a plurality of sidewalls is positioned between thesemiconductor substrate and the transparent sheet. The sidewalls of theframe/spacer collectively have a plan on one side that substantiallycorresponds to, and is substantially in register with, the plan of thefirst frame-attachment area, they have a plan on the opposite side thatsubstantially corresponds to, and is substantially in register with, theplan of the second frame-attachment area, and they have a height thatexceeds the height of the micro-devices. The semiconductor substrate,frame/spacer and transparent sheet are then bonded together to form amulti-package assembly having a plurality of hermetically sealedcavities separated from one another by the frame/spacer sidewalls. Eachof the cavities contains one of the micro-devices positioned below oneof the window aperture portions of the sheet. The multi-package assemblyis divided into individual packages by parting completely through thesubstrate, frame/spacer sidewall and transparent sheet at locationsbetween adjacent cavities. Each individual package thereby encapsulatesone of the micro-devices in a hermetically sealed cavity and includes atransparent window aperture allowing light to pass into and out of thecavity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a hermetically sealed micro-devicepackage;

FIG. 2 is a cross-sectional view of the micro-device package of FIG. 1;

FIG. 3 is an exploded view of a cover assembly manufactured inaccordance with one embodiment of the current invention;

FIGS. 4 a and 4 b show transparent sheets having contoured sides,specifically:

FIG. 4 a showing a sheet having both sides contoured;

FIG. 4 b showing a sheet having one side contoured;

FIG. 5 shows an enlarged view of the sheet seal-ring area prior tometallization;

FIG. 6 shows an enlarged view of the sheet seal-ring area aftermetallization;

FIG. 7 shows a cross-sectional view through a pre-fabricated frame;

FIG. 8 illustrates placing the frame against the metallized sheet priorto bonding;

FIG. 9 is a block diagram of a process for manufacturing coverassemblies using prefabricated frames in accordance with one embodiment;

FIG. 10 is an exploded view of a cover assembly manufactured using asolder preform;

FIG. 11 is a partial perspective view of another embodiment utilizingsolder applied by inkjet;

FIGS. 12 a-c and FIGS. 13 a-c illustrate a process of manufacturingcover assemblies in accordance with yet another embodiment of theinvention, specifically:

FIG. 12 a shows the initial transparent sheet;

FIG. 12 b shows the transparent sheet after initial metallization;

FIG. 12 c shows the transparent sheet after deposition of the integralframe/heat spreader;

FIG. 13 a shows a partial cross-section of the sheet of FIG. 12 a;

FIG. 13 b shows a partial cross-section of the sheet of FIG. 12 b;

FIG. 13 c shows a partial cross-section of the sheet of FIG. 12 c;

FIG. 14 is a block diagram of a process for manufacturing coverassemblies using cold gas dynamic spray technology in accordance withanother embodiment;

FIGS. 15 a-15 b illustrate a multi-unit assembly manufactured inaccordance with another embodiment; specifically:

FIG. 15 a illustrates an exploded view of a the multi-unit assembly;

FIG. 15 b is bottom view of the frame of FIG. 15 a;

FIG. 16 a illustrates compliant tooling formed in accordance withanother embodiment;

FIG. 16 b is a side view of a multi-unit assembly illustrating themethod of separation;

FIGS. 17 a and 17 b illustrate the manufacture of multiple coverassemblies in accordance with yet another embodiment, specifically:

FIG. 17 a shows the transparent sheet in its original state;

FIG. 17 b illustrates the sheet after deposition of the multi-apertureframe/heat spreader;

FIGS. 18 a-18 c illustrate an assembly configuration suitable for usewith electrical resistance heating; specifically:

FIG. 18 a illustrates the configuration of the sheet;

FIG. 18 b illustrates the configuration of the frame;

FIG. 18 c illustrates the joined sheet and frame;

FIGS. 19 a-19 f illustrate multi-unit assembly configurations suitablefor heating with electrical resistance heating;

FIG. 20 a illustrates an exploded view of a window assembly includinginterlayers for diffusion bonding;

FIG. 20 b illustrates the window assembly of FIG. 20 a after diffusionbonding;

FIGS. 20 c and 20 d illustrate an additional embodiment of the inventionhaving internal and external frames; specifically:

FIG. 20 c illustrates an exploded view of a “sandwiched” window assemblybefore bonding;

FIG. 20 d illustrates the completed assembly of FIG. 20 c after bonding;

FIGS. 20 e, 20 f and 20 g, illustrate fixtures for aligning andcompressing the window assemblies during diffusion bonding;specifically:

FIG. 20 e illustrates an empty fixture and clamps;

FIG. 20 f illustrates the fixture of FIG. 20 e with a window assemblypositioned therein for bonding;

FIG. 20 g illustrates an alternative fixture designed to produce moreaxial pressure on the window assembly;

FIGS. 21 a-21 b are cross-sectional views of wafer-level hermeticmicro-device packages in accordance with other embodiments of theinvention; specifically:

FIG. 21 a shows a wafer-level hermetic micro-device packages havingreverse-side electrical connections;

FIG. 21 b shows a wafer-level hermetic micro-device package havingsame-side electrical connections;

FIG. 21 c is an exploded view illustrating the method of assembly of thepackage of FIG. 21 b;

FIG. 22 illustrates a semiconductor wafer having a multiplemicro-devices formed thereupon suitable for multiple simultaneouswafer-level packaging;

FIG. 23 illustrates the semiconductor wafer of FIG. 22 aftermetallization of the wafer surface;

FIG. 24 illustrates a metallic frame for attachment between the wafersurface and the window sheet of a hermetic package;

FIGS. 25 a-25 d show enlarged views of the frame members of FIG. 24;specifically:

FIG. 25 a is a top view of a portion of a double frame member prior tosingulation;

FIG. 25 b is an end view of the double frame member of FIG. 25 a;

FIG. 25 c is a top view of a portion of a single frame member from theperimeter of the frame, or after device singulation; and

FIG. 25 d is an end view of the single frame member of FIG. 25 c;

FIG. 26 illustrates a metallized window sheet for attachment to theframe of FIG. 24;

FIG. 27 shows a cross-sectional side view of a multiple-package assemblyprior to singulation;

FIG. 28 illustrates one option for singulation of the multiple-packageassembly of FIG. 27;

FIG. 29 illustrates another option for singulation of themultiple-package assembly of FIG. 27;

FIG. 30 illustrates a semiconductor wafer after metallization of thewafer surface in accordance with another embodiment having an electrodeplacement portion;

FIG. 31 illustrates a metallized window sheet in accordance with anotherembodiment having an electrode placement portion;

FIG. 32 is a cross-sectional side view of a multiple-package assemblyprior to singulation in accordance with another embodiment having directelectrode access;

FIG. 33 is a top view of a micro-device with same-side pads;

FIG. 34 illustrates a semiconductor wafer having formed thereon aplurality of the micro-devices of FIG. 33;

FIG. 35 illustrates the semiconductor wafer of FIG. 34 aftermetallization of the wafer surface;

FIG. 36 illustrates a metallic frame for attachment to the wafer surfaceof FIG. 35;

FIG. 37 illustrates a metallized window sheet for attachment to theframe of FIG. 36;

FIG. 38 shows a top view a complete multiple-package assembly;

FIG. 39 illustrates a multi-package strip after column separation of themultiple-package assembly of FIG. 38; and

FIG. 40 illustrates a single packaged micro-device after singulation ofthe multiple-package strip of FIG. 39.

DETAILED DESCRIPTION OF THE INVENTION AND BEST MODE

Referring now to FIGS. 1 and 2, there is illustrated a typicalhermetically sealed micro-device package for housing one or moremicro-devices. For purposes of this application, the term “micro-device”includes photonic devices, photovoltaic devices, optical devices (i.e.,including reflective, refractive and diffractive type devices),electro-optical and electro-optics devices (EO devices), light emittingdevices (LEDs), liquid crystal displays (LCDs), liquid crystal onsilicon (LCOS) technologies, which includes direct drive image lightamplifiers (D-ILA), opto-mechanical devices, micro-optoelectromechanicalsystems (i.e., MOEMS) devices and micro-electromechanical systems (i.e.,MEMS) devices. The package 102 comprises a base or substrate 104 that ishermetically sealed to a cover assembly 106 comprising a frame 108 and atransparent window 110. A micro-device 112 mounted on the base 104 isencapsulated within a cavity 114 when the cover assembly 106 is joinedto the base 104. One or more electrical leads 116 may pass through thebase 104 to carry power, ground, and signals to and from themicro-device 112 inside the package 102. It will be appreciated that theelectrical leads 116 must also be hermetically sealed to maintain theintegrity of the package 102. The window 110 is formed of an opticallyor electro-magnetically transparent material. For purposes of thisapplication, the term “transparent” refers to materials that allow thetransmission of electromagnetic radiation having predeterminedwavelengths, including, but not limited to, visible light, infraredlight, ultraviolet light, microwaves, radio waves, or x-rays. The frame108 is formed from a material, typically a metal alloy, which preferablyhas a CTE close to that of both the window 110 and the package base 104.

Referring now to FIG. 3, there is illustrated an exploded view of acover assembly manufactured in accordance with one embodiment of thecurrent invention. The cover assembly 300 includes a frame 302 and asheet 304 of a transparent material. The frame 302 has a continuoussidewall 306 that defines a frame aperture 308 passing therethrough. Theframe sidewall 306 includes a frame seal-ring area 310 (denoted bycrosshatching) circumscribing the frame aperture 308. Since the frame302 will eventually be welded to the package base 104 (from FIGS. 1 and2,) it is usually formed of a weldable metal or alloy, preferably onehaving a CTE very close to that of the micro-device package base 104. Insome embodiments, however, the cover assembly frame 304 may be formed ofa non-metallic material such as ceramic or alumina. Regardless ofwhether the frame 302 is formed of a metallic or non-metallic material,the surface of the frame seal-ring area 310 is preferably metallic(e.g., metal plated if not solid metal) to facilitate the hermeticsealing of the sheet 304 to the frame. In a preferred embodiment, theframe is primarily formed of an alloy having a nominal chemicalcomposition of 54% iron (Fe), 29% nickel (Ni) and 17% cobalt (Co). Suchalloys are also known by the designation ASTM F-15 alloy and by thetrade name Kovar Alloy. As used in this application, the term “KovarAlloy” will be understood to mean the alloy having the chemicalcomposition just described. In embodiments where a Kovar Alloy frame 302is used, it is preferred that the surface of the frame seal-ring area310 have a surface layer of gold (Au) overlying a layer of nickel (Ni),or a layer of nickel without the overlaying gold. The frame 302 alsoincludes a base seal area 320 that is adapted for eventual joining,typically by welding, to the package base 104. The base seal area 320frequently includes a layer of nickel overlaid by a layer of gold tofacilitate seam welding to the package base. Although the gold overnickel surface layers are only required along the base seal-ring area320, it will be appreciated that in many cases, for example, wheresolution bath plating is used to apply the surface materials, the goldover nickel layers may be applied to the entire surface of the frame302. The sheet 304 can be any type of transparent material, for example,soft glass (e.g., soda-lime glass), hard glass (e.g. borosilicateglass), crystalline materials such as quartz and sapphire, or polymericmaterials such as polycarbonate plastic. In addition to opticallytransparent materials, the sheet 304 may be visibly opaque buttransparent to non-visible wavelengths of energy. As previouslydiscussed, it is preferred that the material of the sheet 304 have a CTEthat is similar to that of the frame 304 and of the package base 104 towhich the cover assembly will eventually be attached. For manysemiconductor photonic, photovoltaic, MEMS or MOEMS applications, aborosilicate glass is well suited for the material of the sheet 304.Examples of suitable glasses include Corning 7052, 7050, 7055, 7056,7058, 7062, Kimble (Owens Corning) EN-1, and Kimble K650 and K704. Othersuitable glasses include Abrisa soda-lime glass, Schott 8245 and OharaCorporation S-LAM60.

The sheet 304 has a window portion 312 defined thereupon, i.e., this isthe portion of the sheet 302 which must remain transparent to allow forthe proper functioning of the encapsulated, i.e., packaged, micro-device112. The window portion 312 of the sheet has top and bottom surfaces 314and 316, respectively, that are optically finished in the preferredembodiment. The sheet 304 is preferably obtained with the top and bottomsurfaces 314 and 316 of the window portion 312 in ready to use form,however, if necessary the material may be ground and polished orotherwise shaped to the desired surface contour and finish as apreliminary step of the manufacturing process. While in many cases thewindow portion 312 will have top and bottom surfaces of 314 and 316 thatare optically flat and parallel to one another, it will be appreciatedthat in other embodiments at least one of the finished surfaces of thewindow portion will be contoured. A sheet seal-ring area 318 (denotedwith cross-hatching) circumscribes the window portion 312 of the sheet304, and provides a suitable surface for joining to the front seal-ringarea 310.

Referring now to FIGS. 4 a and 4 b, there are illustrated transparentsheets having contoured sides. In FIG. 4 a, transparent sheet 304′ hasboth a curved top side 314′ and a curved bottom side 316′ producing awindow portion 312 having a curved contour with a constant thickness. InFIG. 4 b, sheet 304″ has a top side 314″ that is curved and a bottomside 316″ that is flat, thereby resulting in a window portion 312 havinga plano-convex lens arrangement. It will be appreciated that in similarfashion (not illustrated) the finished surfaces 314 and 316 of thewindow portion 312 can have the configuration of a refractive lensincluding a plano-convex lens as previously illustrated, a double convexlens, a plano-concave lens or a double concave lens. Other surfacecontours may give the finished surfaces of the window portion 312 theconfiguration of a Fresnel lens or of a diffraction grating, i.e., “adiffractive lens.”

In many applications, it is desirable that window portion 312 of thesheet 304 have enhanced optical or physical properties. To achieve theseproperties, surface treatments or coatings may be applied to the sheet304 prior to or during the assembly process. For example, the sheet 304may be treated with siliconoxynitride (SiOn) to provide a harder surfaceon the window material. Whether or not treated with SiOn, the sheet 304may be coated with a scratch resistant/abrasion resistant material suchas amorphous diamond-like carbon (DLC) such as that sold by Diamonex,Inc., under the name Diamond Shield®. Other coatings which may beapplied in addition to, or instead of, the SiOn or diamond-like carboninclude, but are not limited to, optical coatings, anti-reflectivecoatings, refractive coatings, achromatic coatings, optical filters,solar energy filters or reflectors, electromagnetic interference (EMI)and radio frequency (RF) filters of the type known for use on lenses,windows and other optical elements. It will be appreciated that theoptical coatings and/or surface treatments can be applied either on thetop surface 314 or the bottom surface 316, or in combination on bothsurfaces, of the window portion 312. It will be further appreciated,that the optical coatings and treatments just described are notillustrated in the figures due to their transparent nature.

In some applications, a visible aperture is formed around the windowportion 312 of the sheet 304 by first depositing a layer ofnon-transparent material, e.g., chromium (Cr), sometimes coating thematerial over the entire surface of the sheet and then etching thenon-transparent material from the desired aperture area. This procedureprovides a sharply defined border to the window portion 312 that isdesirable in some applications. This operation may be performed prior toor after the application of other treatments depending on thecompatibility and processing economics.

The next step of the process of manufacturing the cover assembly 300 isto prepare the sheet seal-ring area 318 for metallization. The sheetseal-ring area 318 circumscribes the window portion 312 of the sheet304, and for single aperture covers is typically disposed about theperimeter of the bottom surface 316. It will be appreciated, however,that in some embodiments the sheet seal-ring area 318 can be located inthe interior portion of a sheet, for example where the sheet will bediced to form multiple cover assemblies (i.e., as described laterherein). The sheet seal-ring area 318 generally has a configuration thatclosely matches the configuration of the frame seal-ring area 310 towhich it will eventually be joined. Preparing the sheet seal-ring area318 may involve a thorough cleaning to remove any greases, oils or othercontaminants from the surface, and/or it may involve roughening theseal-ring area by chemical etching, laser ablating, mechanical grindingor sandblasting this area. This roughening increases the surface area ofthe sheet seal-ring, thereby providing increased adhesion for thesubsequently deposited metallization materials, if the sheet seal-ringis to be metallized prior to joining to the frame seal-ring area 310 orto other substrates or device package bases.

Referring now to FIG. 5, there is illustrated a portion of the sheet 304which has been placed bottom side up to better illustrate thepreparation of the sheet seal-ring area 318. In this example theseal-ring area 318 has been given a roughened surface 501 to improveadhesion of the metallic layers to be applied. Chemical etching toroughen glass and similar transparent materials is well known.Alternatively, laser ablating, conventional mechanical grinding orsandblasting may be used. A grinding wheel with 325 grit is believedsuitable for most glass materials, while a diamond grinding wheel may beused for sapphire and other hardened materials. The depth 502 to whichthe roughened surface 501 of the sheet seal-ring area 318 penetrates thesheet 304 is dependent on at least two factors: first, the desiredmounting height of the bottom surface 316 of the window relative to thepackage bottom and/or the micro-device 112 mounted inside the package;and second, the required thickness of the frame 306 including all of thedeposited metal layers (described below). It is believed that etching orgrinding the sheet seal-ring area 318 to a depth of 502 within the rangefrom about 0 inches to about 0.05 inches will provide a satisfactoryadhesion for the metallized layers as well as providing an easilydetectable “lip” for locating the sheet 304 in the proper positionagainst the frame 306 during subsequent joining operations.

It will be appreciated that it may be necessary or desirable to protectthe finished surfaces 314 and/or 316 in the window portion 312 of thesheet (e.g., the portions that will be optically active in the finishedcover assembly) from damage during the roughening process. If so, thesurfaces 314 and/or 316 may be covered with semiconductor-grade “tackytape” or other known masking materials prior to roughening. The maskmaterial must, of course, be removed in areas where the etching/grindingwill take place. Sandblasting is probably the most economical method ofselectively removing strips of tape or masking material in the regionsthat will be roughened. If sandblasting is used, it could simultaneouslyperform the tape removal operation and the roughening of the underlyingsheet.

Referring now to FIG. 6, there is illustrated a view of the seal-ringarea 318 of the sheet 304 after metallization. The next step of themanufacturing process may be to apply one or more metallic layers to theprepared sheet seal-ring area 318. The current invention contemplatesseveral options for accomplishing this metallization. A first option isto apply metal layers to the sheet seal-ring area 318 using conventionalchemical vapor deposition (CVD) technology. CVD technology includesatmospheric pressure chemical vapor deposition (APCVD), low pressurechemical vapor deposition (LPCVD), plasma assisted (enhanced) chemicalvapor deposition (PACVD, PECVD), photochemical vapor deposition (PCVD),laser chemical vapor deposition (LCVD), metal-organic chemical vapordeposition (MOCVD) and chemical beam epitaxy (CBE). A second option formetallizing the roughened seal-ring area 318 is using physical vapordeposition (PVD) technology. PVD technology includes sputtering, ionplasma assist, thermal evaporation, vacuum evaporation, and molecularbeam epitaxy (MBE). A third option for metallizing the roughened sheetseal-ring area 318 is using solution bath plating technology (SBP).Solution bath plating includes electroplating, electroless plating andelectrolytic plating technology. While solution bath plating cannot beused for depositing the initial metal layer onto a nonmetallic surfacesuch as glass or plastic, it can be used for depositing subsequentlayers of metal or metal alloy to the initial layer. Further, it isenvisioned that in many cases, solution bath plating will be the mostcost effective metal deposition technique. Since the use of chemicalvapor deposition, physical vapor deposition and solution bath plating todeposit metals and metal alloys is well known, these techniques will notbe further described herein.

A fourth option for metallizing the sheet seal-ring area 318 of thesheet 304 is so-called cold-gas dynamic spray technology, also known as“cold-spray”. This technology involves the spraying of powdered metals,alloys, or mixtures of metal and alloys onto an article using a jet ofhigh velocity gas to form continuous metallic coating at temperatureswell below the fusing temperatures of the powdered material. Details ofthe cold-gas dynamic spray deposition technology are disclosed in U.S.Pat. No. 5,302,414 to Alkhimov et al. It has been determined thataluminum provides good results when applied to glass using the cold-gasdynamic spray deposition. The aluminum layer adheres extremely well tothe glass and may create a chemical bond in the form of aluminumsilicate. However, other materials may also be applied as a first layerusing cold-spray, including tin, zinc, silver and gold. Since thecold-gas dynamic spray technology can be used at low temperatures (e.g.,near room temperature), it is suitable for metallizing materials havinga relatively low melting point, such as polycarbonates or otherplastics, as well as for metallizing conventional materials such asglass, alumina, and ceramics.

For the initial metallic layer deposited on the sheet 304, it isbelieved that any of chromium, nickel, aluminum, tin, tin-bismuth alloy,gold, gold-tin alloy can be used, this list being given in what isbelieved to be the order of increasing adhesion to glass. Othermaterials might also be appropriate. Any of these materials can beapplied to the sheet seal-ring area 318 using any of the CVD or PVDtechnologies (e.g., sputtering) previously described. After the initiallayer 602 is deposited onto the sheet seal-ring area 318 of thenonmetallic sheet 304, additional metal layers, e.g., second layer 604,third layer 606 and fourth layer 608 (as applicable) can be added by anyof the deposition methods previously described, including solution bathplating. It is believed that the application of the following rules willresult in satisfactory thicknesses for the various metal layers. RuleNo. 1: the minimum thickness, except for the aluminum or tin-basedmetals or alloys that will be bonded to the gold-plated Kovar alloyframe: 0.002 microns. Rule 2: the minimum thickness for aluminum ortin-based metals or alloys deposited onto the sheet or as the finallayer, which will be bonded to the gold-plated Kovar alloy frame: 0.8microns. Rule 3: the maximum thickness for aluminum or tin-based metalsor alloys deposited onto the sheet or as the final layer, which will bebonded to the gold-plated Kovar alloy frame: 63.5 microns. Rule 4: themaximum thickness for metals, other than chromium, deposited onto thesheet as the first layer and which will have other metals or alloysdeposited on top of them: 25 microns. Rule 5: the maximum thickness formetals, other than chromium, deposited onto other metals or alloys asintermediate layers: 6.35 microns. Rule 6: the minimum thickness formetals or alloys deposited onto the sheet or as the final layer, whichwill act as the solder for attachment to the gold-plated Kovar alloyframe: 7.62 microns. Rule 7: the maximum thickness for metals or alloysdeposited onto the sheet or as the final layer, which will act as thesolder for attachment to the gold-plated Kovar alloy frame: 101.6microns. Rule 8: the maximum thickness for chromium: 0.25 microns. Rule9: the minimum thickness for gold-tin solder, applied via inkjet orsupplied as a solder preform: 6 microns. Rule 10: the maximum thicknessfor gold-tin solder, applied via inkjet or supplied as a solder preform:101.6 microns. Rule 11: The minimum thickness for immersion zinc; 0.889microns. Note that the above rules apply to metals deposited using alldeposition methods other than cold-gas dynamic spray deposition.

For cold spray applications, the following rules apply: Rule 1: theminimum practical thickness for any metal layer: 2.54 microns. Rule 2:the maximum practical thickness for the first layer, and all additionallayers, but not including the final Kovar alloy layer: 127 microns. Rule3: the maximum practical thickness for the final Kovar alloy layer:12,700 microns, i.e., 0.5 inches.

By way of example, not to be considered limiting, the following metalcombinations are believed suitable for seal-ring area 318 when bondingthe prepared sheet 304 to a Kovar alloy-nickel-gold frame 302 (i.e.,Kovar alloy core plated first with nickel and then with gold) usingthermal compression (TC) bonding, or sonic, ultrasonic or thermosonicbonding.

The assembly sequence can also be to first bond the frame/spacer andwindow sheet together to form a hermetically sealed window unit, andlater, to bond this window unit to the substrate. A third assemblysequence can also be to first bond the frame/spacer and substratetogether and later, to bond this substrate/frame/spacer unit to thewindow. In some instances, an intermediate material, also referred to asan interlayer material, may be employed between the substrate and theframe/spacer and/or between the frame/spacer and the window sheet. Itwill be understood that, while the examples described herein arebelieved suitable for metallizing the seal-ring surface of a sheet orlens prior to bonding in applications where metallization is used, insome other embodiments employing diffusion bonding (i.e., thermalcompression bonding), metallization of the seal-ring area on the sheetor lens may be omitted altogether when joining the sheet/lens to theframe or another substrate of the device package base.

EXAMPLE 1

Min. Max. Layers Metal Deposition (microns) (microns) 1 Al CVD, PVD 0.763.5

EXAMPLE 2

Min. Max. Layers Metal Deposition (microns) (microns) 1 Al CVD, PVD0.002 25 2 Cu CVD, PVD, SBP 0.002 6.35 3 Ni CVD, PVD, SBP 0.002 6.35 4Sn or SnBi CVD, PVD, SBP 0.7 63.5

EXAMPLE 3

Min. Max. Layers Metal Deposition (microns) (microns) 1 Al CVD, PVD0.002 25 2 Zn CVD, PVD, SBP 0.002 6.35 3 Ni CVD, PVD, SBP 0.002 6.35 4Sn or Sn—Bi CVD, PVD, SBP 0.7 63.5

EXAMPLE 4

Min. Max. Layers Metal Deposition (microns) (microns) 1 Al CVD, PVD0.002 25 2 Zn CVD, PVD, SBP 0.002 6.35 3 Sn or Sn—Bi CVD, PVD, SBP 0.763.5

EXAMPLE 5

Min. Max. Layers Metal Deposition (microns) (microns) 1 Sn (de-stressed)CVD, PVD 0.002 25 2 Cu CVD, PVD, SBP 0.002 6.35 3 Ni CVD, PVD, SBP 0.0026.35 4 Sn or Sn—Bi CVD, PVD, SBP 0.7 63.5

EXAMPLE 6

Min. Max. Layers Metal Deposition (microns) (microns) 1 Sn—Bi CVD, PVD0.7 63.5

EXAMPLE 7

Min. Max. Layers Metal Deposition (microns) (microns) 1 Cr CVD, PVD0.002 0.15 2 Ni CVD, PVD, SBP 0.002 6.35 3 Sn or Sn—Bi CVD, PVD, SBP 0.763.5

EXAMPLE 8

Min. Max. Layers Metal Deposition (microns) (microns) 1 Cr CVD, PVD0.002 0.15 2 Ni CVD, PVD, SBP 0.002 6.35 3 Al CVD, PVD, SBP 0.7 63.5

EXAMPLE 9

Min. Max. Layers Metal Deposition (microns) (microns) 1 Cr CVD, PVD0.002 0.15 2 Ni CVD, PVD, SBP 0.002 6.35 3 Zn CVD, PVD, SBP 0.002 6.35 4Al CVD, PVD, SBP 0.7 63.5

EXAMPLE 10

Min. Max. Layers Metal Deposition (microns) (microns) 1 Ni CVD, PVD0.002 152.4 2 Sn or Sn—Bi CVD, PVD, SBP 0.7 63.5

EXAMPLE 11

Min. Max. Layers Metal Deposition (microns) (microns) 1 Ni CVD, PVD0.002 152.4 2 Al CVD, PVD, SBP 0.7 63.5

EXAMPLE 12

Min. Max. Layers Metal Deposition (microns) (microns) 1 Ni CVD, PVD0.002 152.4 2 Zn CVD, PVD, SBP 0.002 6.35 3 Al CVD, PVD, SBP 0.7 63.5

EXAMPLE 13

Min. Max. Layers Metal Deposition (microns) (microns) 1 Sn CVD, PVD 0.763.5

EXAMPLE 14

Min. Max. Layers Metal Deposition (microns) (microns) 1 Cr CVD, PVD0.002 0.15

EXAMPLE 15

Min. Max. Layers Metal Deposition (microns) (microns) 1 Ni CVD, PVD0.002 152.4

EXAMPLE 16

Min. Max. Layers Metal Deposition (microns) (microns) 1 Sn—Bi CVD, PVD0.7 63.5

By way of further example, not to be considered limiting, the followingmetal combinations and thicknesses are preferred for seal-ring area 318when bonding the prepared sheet 304 to a Kovar alloy-nickel-gold frame302 using thermal compression (TC) bonding, or sonic, ultrasonic orthermosonic bonding.

EXAMPLE 17

Min. Max. Layers Metal Deposition (microns) (microns) 1 Al CVD, PVD 150.8

EXAMPLE 18

Min. Max. Layers Metal Deposition (microns) (microns) 1 Al CVD, PVD 0.12.54 2 Cu CVD, PVD, SBP 0.25 2.54 3 Ni CVD, PVD, SBP 1 5.08 4 Sn or SnBiCVD, PVD, SBP 1 50.8

EXAMPLE 19

Min. Max. Layers Metal Deposition (microns) (microns) 1 Al CVD, PVD 0.12.54 2 Zn CVD, PVD, SBP 0.3175 5.08 3 Ni CVD, PVD, SBP 1 5.08 4 Sn orSn—Bi CVD, PVD, SBP 1 50.8

EXAMPLE 20

Min. Max. Layers Metal Deposition (microns) (microns) 1 Al CVD, PVD 0.12.54 2 Zn CVD, PVD, SBP 0.3175 5.08 3 Sn or Sn—Bi CVD, PVD, SBP 1 50.8

EXAMPLE 21

Min. Max. Layers Metal Deposition (microns) (microns) 1 Sn (de-stressed)CVD, PVD 0.1 2.54 2 Cu CVD, PVD, SBP 0.25 2.54 3 Ni CVD, PVD, SBP 1 5.084 Sn or Sn—Bi CVD, PVD, SBP 1 50.8

EXAMPLE 22

Min. Max. Layers Metal Deposition (microns) (microns) 1 Sn—Bi CVD, PVD 150.8

EXAMPLE 23

Min. Max. Layers Metal Deposition (microns) (microns) 1 Cr CVD, PVD 0.050.12 2 Ni CVD, PVD, SBP 1 5.08 3 Sn or Sn—Bi CVD, PVD, SBP 1 50.8

EXAMPLE 24

Min. Max. Layers Metal Deposition (microns) (microns) 1 Cr CVD, PVD 0.050.12 2 Ni CVD, PVD, SBP 1 5.08 3 Al CVD, PVD, SBP 1 50.8

EXAMPLE 25

Min. Max. Layers Metal Deposition (microns) (microns) 1 Cr CVD, PVD 0.050.12 2 Ni CVD, PVD, SBP 1 5.08 3 Zn CVD, PVD, SBP 0.3175 5.08 4 Al CVD,PVD, SBP 1 50.8

EXAMPLE 26

Min. Max. Layers Metal Deposition (microns) (microns) 1 Ni CVD, PVD 0.15.08 2 Sn or Sn—Bi CVD, PVD, SBP 1 50.8

EXAMPLE 27

Min. Max. Layers Metal Deposition (microns) (microns) 1 Ni CVD, PVD 0.15.08 2 Al CVD, PVD, SBP 1 50.8

EXAMPLE 28

Min. Max. Layers Metal Deposition (microns) (microns) 1 Ni CVD, PVD 0.15.08 2 Zn CVD, PVD, SBP 0.3175 5.08 3 Al CVD, PVD, SBP 1 50.8

EXAMPLE 29

Min. Max. Layers Metal Deposition (microns) (microns) 1 Sn CVD, PVD 150.8

EXAMPLE 30

Min. Max. Layers Metal Deposition (microns) (microns) 1 Cr CVD, PVD 0.050.12

EXAMPLE 31

Min. Max. Layers Metal Deposition (microns) (microns) 1 Ni CVD, PVD 0.150.8

EXAMPLE 32

Min. Max. Layers Metal Deposition (microns) (microns) 1 Sn—Bi CVD, PVD 150.8As indicated above, the previous examples are believed suitable forapplication of, among other processes, thermal compression bonding. TCbonding is a process of diffusion bonding in which two prepared surfacesare brought into intimate contact, and plastic deformation is induced bythe combined effect of pressure and temperature, which in turn resultsin atom movement causing the development of a crystal lattice bridgingthe gap between facing surfaces and resulting in bonding. TC bonding cantake place at significantly lower temperatures than many other forms ofbonding such as braze soldering.

Referring now to FIG. 7, there is illustrated a cross-sectional view ofthe prefabricated frame 302 suitable for use in this embodiment. Theillustrated frame 302 includes a Kovar alloy core 702, or a core ofdifferent metal or alloy, overlaid with a first metallic layer 704 ofnickel that, in turn, is overlaid by an outer layer 706 of gold. The useof Kovar alloy for the core 702 of the frame 302 may be preferred wherehard glass, e.g., Corning 7056 or 7058, is used for the sheet 304 andwhere Kovar alloy or a similar material is used for the package base104, since these materials have a CTE for the temperature range 30° C.to 300° C. that is within the range from about 5.0·10⁻⁶/° K to about5.6·10⁻⁶/° K (e.g. from about 5.0 to about 5.6 ppm/° K).

Referring still to FIG. 7, another step of the manufacturing process isthe preparation of a prefabricated frame 302 for joining to the sheet304. As previously described, the frame 302 includes a continuoussidewall 306 that defines an aperture 308 therethrough. The sidewall 306includes a frame seal-ring area 310 on its upper surface and a baseseal-ring area 320 on its lower surface. The frame seal-ring area 310 isgenerally dimensioned to conform to the sheet seal-ring area 318 of thetransparent sheet 304, while the base seal-ring area 320 is generallydimensioned to conform against the corresponding seal area on thepackage base. The frame 302 may be manufactured using variousconventional metal forming technologies, including stamping, casting,die casting, extrusion/parting, and machining. It is contemplated thatstamping or die-casting may be the most cost effective method forproducing the frames 302. However, fabricating the frame 302 usingphoto-chemical machining (PCM), also known as chemical etching, may, insome instances be the most economical method. In some instances, severalsheets of photo-chemical machined (i.e., etched) metals and/or alloymight be bonded together to form the frame 302. One of the bondingmethods includes TC bonding, also known as diffusion bonding, the PCM'dlayers together to create the frame 302. Depending upon the degree offlatness required for the contemplated bonding procedure and the degreeachieved by a particular frame manufacturing method, surface grinding,and possibly even lapping or polishing, may be required on the frameseal-ring area 310 or base seal-ring area 320, to provide the finalflatness necessary for a successful hermetic seal.

In this example, the base seal-ring area 320 is on the frame faceopposite frame seal-ring area 310, and may utilize the same layers ofnickel 704 overlaid by gold 706 to facilitate eventual welding to thepackage base 104. In some instances, the gold 706 will not be overlaidon the nickel 704.

In some embodiments, the frame 302 will serve as a “heat sink” and/or“heat spreader” when the cover assembly 300 is eventually welded to thepackage base 104. It is contemplated that conventional high temperaturewelding processes (e.g., manual or automatic electrical resistance seamwelding or laser welding) may be used for this operation. If themetallized glass sheet 304 was welded directly to the package base 104using these welding processes, the concentrated heat could cause thermalstresses likely to crack the glass sheet or distort its opticalproperties. However, when a metal frame is attached to the transparentsheet, it acts as both a heat sink, absorbing some of the heat ofwelding, and as a heat spreader, distributing the heat over a wider areasuch that the thermal stress on the transparent sheet 304 is reduced tominimize the likelihood of cracking or optical distortion. Kovar alloyis especially useful in this heat sink and heat spreading role asexplained by Kovar alloy's thermal conductivity, 0.0395, which isapproximately fourteen times higher than the thermal conductivity ofCorning 7052 glass, 0.0028.

Another important aspect of the frame 302 is that it should be formedfrom a material having a CTE that is similar to the CTE of thetransparent sheet 304 and the CTE of the package base 104. This matchingof CTE between the frame 302, transparent sheet 304 and package base 104is beneficial to minimize stresses between these components after theyare joined to one another so as to ensure the long term reliability ofthe hermetic seal therebetween under conditions of thermal cyclingand/or thermal shock environments.

For window assemblies that will be attached to package bases formed ofceramic, alumina or Kovar alloy, Kovar alloy is preferred for use as thematerial for the frame 304. Although Kovar alloy will be used for theframes in many of the embodiments discussed in detail herein, it will beunderstood that Kovar alloy is not necessarily suitable for use with alltransparent sheet materials. Additionally, other frame materials besidesKovar alloy may be suitable for use with glass. Suitability isdetermined by the desire that the material of the transparent sheet 304,the material of the frame 302 and the material of the package base 104all have closely matching CTEs to insure maximum long-term reliabilityof the hermetic seals.

Referring now to FIG. 8, the next step of the manufacturing process isto position the frame 302 against the sheet 304 such that at least aportion of the frame seal-ring area 310 and a least a portion of thesheet seal-ring area 318 contact one another along a continuous junctionregion 804 that circumscribes the window portion 312. Actually, in somecases a plasma-cleaning operation and/or a solvent or detergent cleaningoperation is performed on the seal-ring areas and any other sealingsurfaces just prior to joining the components to ensure maximumreliability of the joint. In FIG. 8, the sheet 304 moves from itsoriginal position (denoted in broken lines) until it is in contact withthe frame 302. It is, of course, first necessary to remove any remainingtacky tape or other masking materials left over from operations used toprepare the sheet seal-ring area 318 if they cannot withstand theelevated temperatures encountered in the joining process withoutdegradation of the mask material and/or its adhesive, if an adhesive isused to attach the mask to the sheet. It will be appreciated that it isnot necessary that the sheet seal-ring area 318 and the frame seal-ringarea 310 have an exact correspondence with regard to their entire areas,rather, it is only necessary that there be some correspondence betweenthe two seal-ring areas forming a continuous junction region 804 whichcircumscribes the window portion 312. In the embodiment illustrated inFIG. 8, the metallized layers 610 in the sheet seal-ring area 318 aremuch wider than the plated outer layer 706 of the frame seal-ring area310. Further, the window portion 312 of the sheet 304 extends partwaythrough the frame aperture 308, providing a means to center the sheet304 on the frame 302.

The next step of the manufacturing process is to heat the junctionregion 804 until a joint is formed between the frame 302 and the sheet304 all along the junction region, whereby a hermetic sealcircumscribing the window portion 312 is formed. It is necessary thatduring the step of heating the junction region 804, the temperature ofthe window portion 312 of the sheet 304 remain below its glasstransition temperature, T_(G) as well as below the softening temperatureof the sheet 304, to prevent damage to the finished surfaces 314 and316. The softening point for glass is defined as the temperature atwhich the glass has a viscosity of 107.6 dPa s or 107.6 poise (method ofmeasurement: ISO 7884-3). The current invention contemplates severaloptions for accomplishing this heating. A first option is to utilizethermal compression (TC) bonding, also known as diffusion bonding,including conventional hot press bonding as well as Hot Isostatic Pressor Hot Isostatic Processing (HIP) diffusion bonding. As previouslydescribed, TC bonding, also known as diffusion bonding involves theapplication of high pressures to the materials being joined such that areduced temperature is required to produce the necessary diffusion bond.Rules for determining the thickness and composition of the metalliclayers 610 on the sheet 304 were previously provided, for TC bonding to,e.g., a Kovar alloy, nickel or gold frame such as illustrated in FIG. 7.The estimated process parameters for the TC bonding of a Kovaralloy/nickel/gold frame 302 to a metallized sheet 304 having aluminum asthe final layer would be a temperature of approximately 380° C. at anapplied pressure of approximately 95,500 psi (6713.65 kg/cm²). Underthese conditions, the gold plating 706 on the Kovar alloy frame 302 willdiffuse into/with the aluminum layer, e.g., layer 4 in Example 7. Sincethe 380° C. temperature necessary for TC bonding is below theapproximately 500° C. to 900° C. T_(G) for hard glasses such as Corning7056, the TC bonding process could be performed in a single or batchmode by fixturing the cover assembly components 302, 304 together incompression and placing the compressed assemblies into a furnace (oroven, etc.) at approximately 380° C. The hermetic bond would be obtainedwithout risking the finished surfaces 314 and 316 of the window portion312. Vacuum, sometimes with some small amounts of specific gassesincluded, or other atmospheres with negative or positive pressures mightbe needed inside the furnace to promote the TC bonding process.

Alternatively, employing resistance welding at the junction area 804 toadd additional heat in addition to the TC bonding could allow preheatingthe window assemblies to less than 380° C. and possibly reduce theoverall bonding process time. In another method, the TC bonding could beaccomplished by fixturing the cover assembly components 302 and 304using heated tooling that would heat the junction area 304 byconduction. In yet another alternative method, electrical resistancewelding can be used to supply 100% of the heat required to achieve thenecessary TC bonding temperature, thereby eliminating the need forfurnaces, ovens, etc. or specialized thermally conductive tooling.

After completion of TC bonding or other welding processes, the windowassembly 300 is ready for final processing, for example, chamfering theedges of the cover assembly to smooth them and prevent chipping,scratching, marking, etc., during post-assembly, cleaning, marking orother operations. In some instances, the final processing may includethe application of a variety of coatings to the window and/or to theframe.

Referring now to FIG. 9, there is illustrated a block diagram of themanufacturing process just described in accordance with one embodimentof the current invention. Block 902 represents the step of obtaining asheet of transparent material, e.g., glass or other material, havingfinished top and bottom surfaces as previously described. The processthen proceeds to block 904 as indicated by the arrow.

Block 904 represents the step of applying surface treatments to thesheet, e.g., scratch-resistant or anti-reflective coatings, aspreviously described. In addition to these permanent surface treatments,block 904 also represents the sub-steps of applying tape or othertemporary masks to the surfaces of the sheet to protect them during thesubsequent steps of the process. It will be appreciated that the stepsrepresented by block 904 are optional and that one or more of thesesteps may not be present in every embodiment of the invention. Theprocess then proceeds to block 906 as indicated by the arrow.

Block 906 represents the step of preparing the seal-ring area on thesheet to provide better adhesion for the metallic layers, if suchmetallic layers are used. This step usually involves roughening theseal-ring area using chemical etching, mechanical grinding, laserablating or sandblasting as previously described. To the extentnecessary, block 906 also represents the sub-steps of removing anymasking material from the seal-ring area. Block 906 further representsthe optional steps of cleaning the sheet (or at least the seal-ring areaof the sheet) to remove any greases, oils or other contaminants from thesurface of the sheet. As previously discussed, such cleaning steps maybe performed regardless of whether the seal-ring area is to bemetallized (i.e., to promote better adhesion of the metallic layers) oris to be left unmetallized (i.e., to promote better diffusion bonding ofthe unmetallized sheet). It will be appreciated that the stepsrepresented by block 906 are optional and that some or all of thesesteps may not be present in every embodiment of the invention. Theprocess then proceeds to block 908 as indicated by the arrow.

Block 908 represents the step of metallizing the seal-ring areas of thesheet. The step represented by block 908 is mandatory only when thedesired bond of sheet 304 to frame 302 is a metal-to-metal bond since atleast one metallic layer must be applied to the seal-ring area of thesheet. It is possible, for instance by use of diffusion bondingprocesses, to bond the sheet 304 to frame 302 without first metallizingsheet 304. In most embodiments, block 908 will represent numeroussub-steps for applying successive metallic layers to the sheet, wherethe layers of each sub-step may be applied by processes including CVD,PVD, cold-spray or solution bath plating as previously described.Following the steps represented by block 908, the sheet is ready forjoining to the frame. However, before the process can proceed to thisjoining step (i.e., block 916), a suitable frame must first be prepared.

Block 910 represents the step of obtaining a pre-fabricated frame,preferably having a CTE that closely matches the CTE of the transparentsheet from block 902 and the CTE of the package base. In most caseswhere the base is alumina or Kovar alloy, a frame formed of Kovar alloywill be suitable. As previously described, the frame may be formedusing, e.g., stamping, die-casting or other known metal-formingprocesses. The process then proceeds to block 912 as indicated by thearrow.

Block 912 represents the step of grinding, polishing and/or otherwiseflattening the seal-ring areas of the frame as necessary to increase itsflatness so that it will fit closely against the seal-ring areas of thetransparent sheet. It will be appreciated that the steps represented byblock 912 are optional and may not be necessary or present in everyembodiment of the invention. The process then proceeds to block 914 asindicated by the arrow.

Block 914 represents the step of applying additional metallic layers tothe seal-ring areas of the frame. These metallic layers are sometimesnecessary to achieve compatible chemistry for bonding with themetallized seal-ring areas of the transparent sheet. In mostembodiments, block 914 will represent numerous sub-steps for applyingsuccessive metallic layers to the frame. Block 914 further representsthe optional steps of cleaning the frame (or at least the seal-ring areaof the frame) to remove any greases, oils or other contaminants from thesurface of the frame. As previously discussed, such cleaning steps maybe performed regardless of whether the seal-ring area of the frame is tobe metallized with additional metal layers or is to be used withoutadditional metallization. Once the steps represented by block 914 arecompleted, the frame is ready for joining to the transparent sheet.Thus, the results of process block 908 and block 914 both proceed toblock 916 as indicated by the arrows.

Block 916 represents the step of clamping the prepared frame togetherwith the prepared transparent sheet so that their respective metallizedseal-ring areas are in contact with one another under conditionsproducing a predetermined contact pressure at the junction regioncircumscribing the window portion. This predetermined contact pressurebetween the seal-ring surfaces allows thermal compression (TC) bondingof the metallized surfaces to occur at a lower temperature than would berequired for conventional welding (including most soldering and brazingprocesses). The process then proceeds to block 918 as indicated by thearrow.

Block 918 represents the step of applying heat to the junction betweenthe frame and the transparent sheet while maintaining the predeterminedcontact pressure until the temperature is sufficient to cause thermalcompression bonding to occur. In some embodiments, block 918 willrepresent a single heating step, e.g., heating the fixtured assembly ina furnace. In other embodiments, block 918 will represent severalsub-steps for applying heat to the junction area, for example, firstpreheating the fixtured assembly (e.g., in a furnace) to an intermediatetemperature, and then using resistance welding techniques along thejunction to raise the temperature of the localized area of the metalliclayers the rest of the way to the temperature where thermal compressionbonding will occur. The thermal compression bonding creates a hermeticseal between the transparent sheet material and the frame. The processthen proceeds to block 920 as indicated by the arrow.

In the illustrated example, metallized seal-ring areas are joined usingdiffusion bonding/thermal compression bonding in which the predeterminedpressure is applied first (block 916) and the heat is applied second(block 918). It will be appreciated, however, that the use of diffusionbonding is not limited to these specific conditions. In some otherembodiments, the sheet and/or frame may not be metallized prior tobonding. In still other embodiments, the heat may be applied first untilthe desired bonding temperature is reached, and the predeterminedpressure may be applied thereafter until the diffusion bond is formed.In yet additional embodiments, the heat and pressure may be appliedsimultaneously until the diffusion bond is formed.

Block 920 represents the step of completing the window assembly. Block920 may represent merely cooling the window assembly after thermalcompression bonding, or it may represent additional finishing processesincluding chamfering the edges of the assembly to prevent chipping,cracking, etc., marking the assembly, coating the window and/or theframe with one or more materials, or other post-assembly procedures. Theprocess of this embodiment has thus been described.

It will be appreciated that in alternative embodiments of the invention,conventional welding techniques (including soldering and/or brazing) maybe used instead of thermal compression bonding to join the frame to thetransparent sheet. In such alternative embodiments, the stepsrepresented by blocks 916 and 918 of FIG. 9 would be replaced by thesteps of fixturing the frame and transparent sheet together so that themetallized seal-ring areas are in contact with one another (but notnecessarily producing a predetermined contact pressure along thejunction) and then applying heat to the junction area using conventionalmeans until the temperature is sufficient to cause the melting anddiffusing of the metallic layers necessary to achieve the welded bond.

In an alternative embodiment, braze-soldering is used to join the frame302 to the metallized sheet 304. In this embodiment, a solder metal orsolder alloy may be utilized as the final layer of the metallic layers610 on the metallized sheet 304, and clamping the sheet 304 to the frame302 at a high predetermined contact pressure is not required. A soldermetal or solder alloy preform may be utilized as a separate,intermediate item between the frame 302 and the sheet 304 instead ofhaving a solder metal or solder alloy as the final layer of the metalliclayers 610 on the metallized sheet 304. Light to moderate clampingpressure can be used: 1) to insure alignment during the solder's moltenphase; and 2) to promote even distribution of the molten solder allalong the junction region between the respective seal-ring areas;thereby helping to insure a hermetic seal, however, this clampingpressure does not contribute to the bonding process itself as in TCbonding. In most other respects, however, this embodiment issubstantially similar to that previously described.

The following examples, not to be considered limiting, are provided toillustrate the details of the metallic layers 610 in the sheet seal-ringarea 318 that are suitable for braze-soldering to a Kovaralloy/nickel/gold frame 302 such as that illustrated in FIG. 7.

EXAMPLE 33

Min. Max. Layers Metal Deposition (microns) (microns) 1 Al CVD, PVD0.002 25 2 Cu CVD, PVD, SBP 0.002 6.35 3 Ni CVD, PVD, SBP 0.002 6.35 4Eutectic Au—Sn CVD, PVD, SBP 1.27 127 solder

EXAMPLE 34

Min. Max. Layers Metal Deposition (microns) (microns) 1 Al CVD, PVD0.002 25 2 Cu CVD, PVD, SBP 0.002 6.35 3 Ni CVD, PVD, SBP 0.002 6.35 4Sn—Bi solder CVD, PVD, SBP 1.27 152.4

EXAMPLE 35

Min. Max. Layers Metal Deposition (microns) (microns) 1 Al CVD, PVD0.002 25 2 Zn CVD, PVD, SBP 0.002 6.35 3 Ni CVD, PVD, SBP 0.002 6.35 4Eutectic Au—Sn CVD, PVD, SBP 1.27 127 solder

EXAMPLE 36

Min. Max. Layers Metal Deposition (microns) (microns) 1 Al CVD, PVD0.002 25 2 Zn CVD, PVD, SBP 0.002 6.35 3 Ni CVD, PVD, SBP 0.002 6.35 4Sn—Bi solder CVD, PVD, SBP 1.27 152.4

EXAMPLE 37

Min. Max. Layers Metal Deposition (microns) (microns) 1 Cr CVD, PVD0.002 0.15 2 Zn CVD, PVD, SBP 0.002 6.35 3 Ni CVD, PVD, SBP 0.002 6.35 4Eutectic Au—Sn CVD, PVD, SBP 1.27 127 solder

EXAMPLE 38

Min. Max. Layers Metal Deposition (microns) (microns) 1 Cr CVD, PVD0.002 0.15 2 Ni CVD, PVD, SBP 0.002 6.35 3 Eutectic Au—Sn CVD, PVD, SBP1.27 127 solder

EXAMPLE 39

Min. Max. Layers Metal Deposition (microns) (microns) 1 Cr CVD, PVD0.002 0.15 2 Zn CVD, PVD, SBP 0.002 6.35 3 Ni CVD, PVD, SBP 0.002 6.35 4Sn—Bi solder CVD, PVD, SBP 1.27 152.4

EXAMPLE 40

Min. Max. Layers Metal Deposition (microns) (microns) 1 Cr CVD, PVD0.002 0.15 2 Ni CVD, PVD, SBP 0.002 6.35 3 Sn—Bi solder CVD, PVD, SBP1.27 152.4

EXAMPLE 41

Min. Max. Layers Metal Deposition (microns) (microns) 1 Cr CVD, PVD0.002 0.15 2 Sn—Bi solder CVD, PVD, SBP 1.27 152.4

EXAMPLE 42

Min. Max. Layers Metal Deposition (microns) (microns) 1 De-stressed SnCVD, PVD 1.27 152.4 Solder

EXAMPLE 43

Min. Max. Layers Metal Deposition (microns) (microns) 1 Sn—Bi SolderCVD, PVD 1.27 152.4

EXAMPLE 44

Min. Max. Layers Metal Deposition (microns) (microns) 1 Eutectic Au—SnCVD, PVD 1.27 127 Solder

EXAMPLE 45

Min. Max. Layers Metal Deposition (microns) (microns) 1 Ni CVD, PVD0.002 152.4 2 Eutectic Au—Sn CVD, PVD, SBP 1.27 127 Solder

EXAMPLE 46

Min. Max. Layers Metal Deposition (microns) (microns) 1 Ni CVD, PVD0.002 152.4 2 Sn—Bi Solder CVD, PVD, SBP 1.27 152.4

While numerous examples herein show the use of eutectic Au—Sn, otherapplications may utilize non-eutectic Au—Sn, or other eutectic ornon-eutectic solders for attaching the window. This allows subsequentuse of a higher melting temperature solder to attach the unit to ahigher level assembly without melting the window bond.

By way of further examples, not to be considered limiting, the followingcombinations are preferred for the metallic layers 610 in the sheetseal-ring area 318 for braze-soldering to a Kovar alloy/nickel/goldframe 302 such as that illustrated in FIG. 7.

EXAMPLE 47

Min. Max. Layers Metal Deposition (microns) (microns) 1 Al CVD, PVD 0.12.54 2 Cu CVD, PVD, SBP 0.25 2.54 3 Ni CVD, PVD, SBP 1 5.08 4 EutecticAu—Sn CVD, PVD, SBP 2.54 63.5 solder

EXAMPLE 47a

Min. Max. Layers Metal Deposition (microns) (microns) 1 Al CVD, PVD 0.12.54 2 Cu CVD, PVD, SBP 0.25 2.54 3 Ni CVD, PVD, SBP 1 5.08 4 Sn—Cu—AgSolder CVD, PVD, SBP 2.54 63.5

EXAMPLE 48

Min. Max. Layers Metal Deposition (microns) (microns) 1 Al CVD, PVD 0.12.54 2 Cu CVD, PVD, SBP 0.25 2.54 3 Ni CVD, PVD, SBP 1 5.08 4 Sn—Bisolder CVD, PVD, SBP 2.54 127

EXAMPLE 49

Min. Max. Layers Metal Deposition (microns) (microns) 1 Al CVD, PVD 0.12.54 2 Zn CVD, PVD, SBP 0.3175 5.08 3 Ni CVD, PVD, SBP 1 5.08 4 EutecticAu—Sn CVD, PVD, SBP 2.54 63.5 solder

EXAMPLE 49a

Min. Max. Layers Metal Deposition (microns) (microns) 1 Al CVD, PVD 0.12.54 2 Zn CVD, PVD, SBP 0.3175 5.08 3 Ni CVD, PVD, SBP 1 5.08 4 Sn—Cu—AgSolder CVD, PVD, SBP 2.54 63.5

EXAMPLE 50

Min. Max. Layers Metal Deposition (microns) (microns) 1 Al CVD, PVD 0.12.54 2 Zn CVD, PVD, SBP 0.3175 5.08 3 Ni CVD, PVD, SBP 1 5.08 4 Sn—Bisolder CVD, PVD, SBP 2.54 127

EXAMPLE 51

Min. Max. Layers Metal Deposition (microns) (microns) 1 Cr CVD, PVD 0.050.12 2 Zn CVD, PVD, SBP 0.3175 5.08 3 Ni CVD, PVD, SBP 1 5.08 4 EutecticAu—Sn CVD, PVD, SBP 2.54 63.5 solder

EXAMPLE 51a

Min. Max. Layers Metal Deposition (microns) (microns) 1 Cr CVD, PVD 0.050.12 2 Zn CVD, PVD, SBP 0.3175 5.08 3 Ni CVD, PVD, SBP 1 5.08 4 Sn—Cu—AgSolder CVD, PVD, SBP 2.54 63.5

EXAMPLE 52

Min. Max. Layers Metal Deposition (microns) (microns) 1 Cr CVD, PVD 0.050.12 2 Ni CVD, PVD, SBP 1 5.08 3 Eutectic Au—Sn CVD, PVD, SBP 2.54 63.5solder

EXAMPLE 52a

Min. Max. Layers Metal Deposition (microns) (microns) 1 Cr CVD, PVD 0.050.12 2 Ni CVD, PVD, SBP 1 5.08 3 Sn—Cu—Ag Solder CVD, PVD, SBP 2.54 63.5

EXAMPLE 53

Min. Max. Layers Metal Deposition (microns) (microns) 1 Cr CVD, PVD 0.050.12 2 Zn CVD, PVD, SBP 0.3175 5.08 3 Ni CVD, PVD, SBP 1 5.08 4 Sn—Bisolder CVD, PVD, SBP 2.54 127

EXAMPLE 54

Min. Max. Layers Metal Deposition (microns) (microns) 1 Cr CVD, PVD 0.050.12 2 Ni CVD, PVD, SBP 1 5.08 3 Sn—Bi solder CVD, PVD, SBP 2.54 127

EXAMPLE 55

Min. Max. Layers Metal Deposition (microns) (microns) 1 Cr CVD, PVD 0.050.12 2 Sn—Bi solder CVD, PVD, SBP 2.54 127

EXAMPLE 56

Min. Max. Layers Metal Deposition (microns) (microns) 1 De-stressed SnCVD, PVD 2.54 127 Solder

EXAMPLE 57

Min. Max. Layers Metal Deposition (microns) (microns) 1 Sn—Bi SolderCVD, PVD 2.54 127

EXAMPLE 58

Min. Max. Layers Metal Deposition (microns) (microns) 1 Eutectic Au—SnCVD, PVD 2.54 63.5 Solder

EXAMPLE 58a

Min. Max. Layers Metal Deposition (microns) (microns) 1 Sn—Cu—Ag SolderCVD, PVD 2.54 63.5

EXAMPLE 59

Min. Max. Layers Metal Deposition (microns) (microns) 1 Ni CVD, PVD 0.15.08 2 Eutectic Au—Sn CVD, PVD, SBP 2.54 63.5 Solder

EXAMPLE 59a

Min. Max. Layers Metal Deposition (microns) (microns) 1 Ni CVD, PVD 0.15.08 2 Sn—Cu—Ag Solder CVD, PVD, SBP 2.54 63.5

EXAMPLE 60

Min. Max. Layers Metal Deposition (microns) (microns) 1 Ni CVD, PVD 0.15.08 2 Sn—Bi Solder CVD, PVD, SBP 2.54 127

Referring now to FIG. 10, there is illustrated yet another embodiment ofthe current invention. Note that in this embodiment, the cover assembly300 is circular in configuration rather than rectangular. It will beappreciated that this is simply another possible configuration for acover assembly manufactured in accordance with this invention, and thatthis embodiment is not limited to configurations of any particularshape. As in the embodiment previously described, this embodiment alsouses braze-soldering to hermetically join the transparent sheet 304 tothe frame 302. However, in this embodiment, the solder for brazesoldering is provided in the form of a separate solder preform 1000having the shape of the sheet seal-ring area 318 or the frame seal-ringarea 310. Also in this embodiment, preform 1000 can be of materialsother than solder for use as an innerlayer or interlayer materialbetween the transparent sheet 304 and the frame 302. When used as theinnerlayer or interlayer for TC bonding, one or more elements of preform1000 diffuses with one or more elements of sheet 304 and the frame 302.

In this embodiment, when the preform solder 1000 is used forbraze-soldering to hermetically join the transparent sheet 304 to theframe 302, instead of positioning the frame and the sheet directlyagainst one another, the frame 302 and the sheet 304 are insteadpositioned against opposite sides of the solder preform 1000 such thatthe solder preform is interposed between the frame seal-ring area 310and the sheet seal-ring are 318 along a continuous junction region thatcircumscribes the window portion 312. After the frame 302 and sheet 304are positioned against the solder preform 1000, the junction region isheated until the solder preform fuses forming a solder joint between theframe and sheet all along the junction region. The heating of thejunction region may be performed by any of the procedures previouslydescribed, including heating or preheating in a furnace, oven, etc.,either alone or in combination with other heating methods includingresistance welding. It is required that during the step of heating thejunction region, the temperature of the window portion 312 of the sheet304 remain below the glass transition temperature T_(G) and thesoftening temperature such that the finished surfaces 314 and 316 on thesheet are not adversely affected.

The current embodiment using a solder preform 1000 can be used forjoining a metallized sheet 304 to a Kovar alloy/nickel/gold frame suchas that illustrated in FIG. 7. In accordance with a preferredembodiment, the solder preform 1000 is formed of a gold-tin (Au—Sn)alloy, and in a more preferred embodiment, the gold-tin alloy is theeutectic composition. One of the alternative alloys for preform 1000 istin-copper-silver (Sn—Cu—Ag). The thickness of the gold-tin preform 1000will probably be within the range from about 6 microns to about 101.2microns. The thickness of other alloys for preform 1000 will alsoprobably be within the range of about 6 microns to about 101.2 microns.

The following examples, not to be considered limiting, are provided toillustrate the details of the metallic layers 610 and the sheetseal-ring area 318 that are suitable for braze-soldering to a Kovaralloy/nickel/gold frame in combination with a gold-tin solder preform orother suitable solder alloy preforms, including, but not limited totin-copper-silver alloys.

EXAMPLE 61

Min. Max. Layers Metal Deposition (microns) (microns) 1 Al CVD, PVD0.002 25 2 Cu CVD, PVD, SBP 0.002 6.35 3 Ni CVD, PVD, SBP 0.002 6.35 4Au CVD, PVD, SBP 0.0508 0.508

EXAMPLE 62

Min. Max. Layers Metal Deposition (microns) (microns) 1 Al CVD, PVD0.002 25 2 Cu CVD, PVD, SBP 0.002 6.35 3 Ni CVD, PVD, SBP 0.002 6.35 4Sn—Bi CVD, PVD, SBP 0.635 12.7

EXAMPLE 63

Min. Max. Layers Metal Deposition (microns) (microns) 1 Al CVD, PVD0.002 25 2 Zn CVD, PVD, SBP 0.002 6.35 3 Ni CVD, PVD, SBP 0.002 6.35 4Au CVD, PVD, SBP 0.0508 0.508

EXAMPLE 64

Min. Max. Layers Metal Deposition (microns) (microns) 1 Al CVD, PVD0.002 25 2 Zn CVD, PVD, SBP 0.002 6.35 3 Ni CVD, PVD, SBP 0.002 6.35 4Sn—Bi CVD, PVD, SBP 0.635 12.7

EXAMPLE 65

Min. Max. Layers Metal Deposition (microns) (microns) 1 Cr CVD, PVD0.002 0.15 2 Zn CVD, PVD, SBP 0.002 6.35 3 Ni CVD, PVD, SBP 0.002 6.35 4Au CVD, PVD, SBP 0.0508 0.508

EXAMPLE 66

Min. Max. Layers Metal Deposition (microns) (microns) 1 Cr CVD, PVD0.002 0.15 2 Ni CVD, PVD, SBP 0.002 6.35 3 Au CVD, PVD, SBP 0.0508 0.508

EXAMPLE 67

Min. Max. Layers Metal Deposition (microns) (microns) 1 Cr CVD, PVD0.002 0.15 2 Zn CVD, PVD, SBP 0.002 6.35 3 Ni CVD, PVD, SBP 0.002 6.35 4Sn—Bi CVD, PVD, SBP 0.635 12.7

EXAMPLE 68

Min. Max. Layers Metal Deposition (microns) (microns) 1 Cr CVD, PVD0.002 0.15 2 Ni CVD, PVD, SBP 0.002 6.35 3 Sn—Bi CVD, PVD, SBP 0.63512.7

EXAMPLE 69

Min. Max. Layers Metal Deposition (microns) (microns) 1 Cr CVD, PVD0.002 0.15 2 Sn—Bi CVD, PVD, SBP 0.635 12.7

EXAMPLE 70

Min. Max. Layers Metal Deposition (microns) (microns) 1 Cr CVD, PVD0.002 0.15

EXAMPLE 71

Min. Max. Layers Metal Deposition (microns) (microns) 1 De-stressed SnCVD, PVD 0.635 12.7 or Sn—Bi

EXAMPLE 72

Min. Max. Layers Metal Deposition (microns) (microns) 1 Au CVD, PVD0.0508 0.508

EXAMPLE 73

Min. Max. Layers Metal Deposition (microns) (microns) 1 Ni CVD, PVD0.002 152.4 2 Au CVD, PVD, SBP 0.0508 0.508

EXAMPLE 74

Min. Max. Layers Metal Deposition (microns) (microns) 1 Ni CVD, PVD0.002 152.4 2 Sn—Bi CVD, PVD, SBP 0.635 12.7

EXAMPLE 75

Min. Max. Layers Metal Deposition (microns) (microns) 1 Ni CVD, PVD0.002 152.4 2 Sn (De-stressed CVD, PVD, SBP 0.635 12.7 after deposition)

By way of further examples, not to be considered limiting, the followingcombinations are preferred for the metallic layers 610 and the sheetseal-ring area 318 for braze-soldering to a Kovar alloy/nickel/goldframe in combination with a gold-tin soldered preform. In addition tohaving a frame of Kovar alloy/nickel/gold, materials other than Kovarmay be employed as the frame's base material and the overlying layer orlayers may be nickel without the gold, or combinations of two or moremetals including, but not limited to nickel and gold.

EXAMPLE 76

Min. Max. Layers Metal Deposition (microns) (microns) 1 Al CVD, PVD 0.12.54 2 Cu CVD, PVD, SBP 0.25 2.54 3 Ni CVD, PVD, SBP 1 5.08 4 Au CVD,PVD, SBP 0.127 0.381

EXAMPLE 77

Min. Max. Layers Metal Deposition (microns) (microns) 1 Al CVD, PVD 0.12.54 2 Cu CVD, PVD, SBP 0.25 2.54 3 Ni CVD, PVD, SBP 1 5.08 4 Sn—Bi CVD,PVD, SBP 2.54 7.62

EXAMPLE 78

Min. Max. Layers Metal Deposition (microns) (microns) 1 Al CVD, PVD 0.12.54 2 Zn CVD, PVD, SBP 0.3175 5.08 3 Ni CVD, PVD, SBP 1 5.08 4 Au CVD,PVD, SBP 0.127 0.381

EXAMPLE 79

Min. Max. Layers Metal Deposition (microns) (microns) 1 Al CVD, PVD 0.12.54 2 Zn CVD, PVD, SBP 0.3175 5.08 3 Ni CVD, PVD, SBP 1 5.08 4 Sn—BiCVD, PVD, SBP 2.54 7.62

EXAMPLE 80

Min. Max. Layers Metal Deposition (microns) (microns) 1 Cr CVD, PVD 0.050.12 2 Zn CVD, PVD, SBP 0.3175 5.08 3 Ni CVD, PVD, SBP 1 5.08 4 Au CVD,PVD, SBP 0.127 0.381

EXAMPLE 81

Min. Max. Layers Metal Deposition (microns) (microns) 1 Cr CVD, PVD 0.050.12 2 Ni CVD, PVD, SBP 1 5.08 3 Au CVD, PVD, SBP 0.127 0.381

EXAMPLE 82

Min. Max. Layers Metal Deposition (microns) (microns) 1 Cr CVD, PVD 0.050.12 2 Zn CVD, PVD, SBP 0.3175 5.08 3 Ni CVD, PVD, SBP 1 5.08 4 Sn—BiCVD, PVD, SBP 2.54 7.62

EXAMPLE 83

Min. Max. Layers Metal Deposition (microns) (microns) 1 Cr CVD, PVD 0.050.12 2 Ni CVD, PVD, SBP 1 5.08 3 Sn—Bi CVD, PVD, SBP 2.54 7.62

EXAMPLE 84

Min. Max. Layers Metal Deposition (microns) (microns) 1 Cr CVD, PVD 0.050.12 2 Sn—Bi CVD, PVD, SBP 2.54 7.62

EXAMPLE 85

Min. Max. Layers Metal Deposition (microns) (microns) 1 Cr CVD, PVD 0.050.12

EXAMPLE 86

Min. Max. Layers Metal Deposition (microns) (microns) 1 De-stressed SnCVD, PVD 2.54 7.62 or Sn—Bi

EXAMPLE 87

Min. Max. Layers Metal Deposition (microns) (microns) 1 Au CVD, PVD0.127 0.381

EXAMPLE 88

Min. Max. Layers Metal Deposition (microns) (microns) 1 Ni CVD, PVD 0.15.08 2 Au CVD, PVD, SBP 0.127 0.381

EXAMPLE 89

Min. Max. Layers Metal Deposition (microns) (microns) 1 Ni CVD, PVD 0.15.08 2 Sn—Bi CVD, PVD, SBP 2.54 7.62

EXAMPLE 90

Min. Max. Layers Metal Deposition (microns) (microns) 1 Ni CVD, PVD 0.15.08 2 Sn (De-stressed CVD, PVD, SBP 2.54 7.62 after deposition)

Referring now to FIG. 11, there is illustrated yet another embodiment ofthe current invention. This embodiment also uses soldering, however, inthis embodiment the solder is applied via inkjet technology to eitherthe metallized area 610 in the sheet seal-ring area 318 or the sheetseal-ring 310 of the frame assembly. FIG. 11 shows a portion of theKovar alloy/nickel/gold frame 302 (or other frame alloy and overlayercombination) and an inkjet dispensing head 1102 which is dispensingoverlapping drops of solder 1104 onto the frame seal-ring area 310 asthe dispensing head moves around the frame aperture 308 or the frameaperture is moved underneath the dispensing head, as indicated by arrow1106. Preferably, the inkjet dispensed solder is a gold-tin (Au—Sn)alloy, and more preferably it is the eutectic composition. The preferredthickness of the gold-tin solder applied by dispensing head 1102 in thisembodiment is within the range from about 6 microns to about 101.2microns. It will be appreciated that while the example illustrated inFIG. 11 shows the dispensing head 1102 depositing the solder droplets1104 onto the frame 302, in other embodiments the inkjet depositedsolder may be applied to the sheet seal-ring area 318, either alone orin combination with applications on the frame seal-ring area 310. Instill other embodiments, the inkjet deposited solder may be used tocreate a discrete solder preform that would be employed as described inthe previous examples herein. In still other embodiments, the inkjetdeposited material, which may or may not be solder, may be used tocreate an innerlayer or interlay preform that would be employed for usein TC bonding or HIP diffusion bonding as described in previous examplesherein. Details of the metallic layers 610 in the sheet seal-ring area318 that are suitable for a soldering to a Kovar alloy/nickel/gold frame302 such as that illustrated in FIG. 7 using inkjet supplied solder aresubstantially identical to those layers illustrated in previous Examples21 through 32.

Referring now to FIGS. 12 a through 12 c and FIGS. 13 a through 13 c,there is illustrated yet another alternative method for manufacturingcover assemblies constituting another embodiment of the currentinvention. Whereas, in the previous embodiments a separate prefabricatedmetal frame was joined to the transparent sheet to act as a heatspreader/heat sink needed for subsequent welding, in this embodiment acold gas dynamic spray deposition process is used to fabricate ametallic frame/heat spreader directly on the transparent sheet material.In other words, in this embodiment the frame is fabricated directly onthe transparent sheet as an integral part, no subsequent joiningoperation is required. In addition, since cold gas dynamic spraydeposition can be accomplished at near room temperature, this method isespecially useful where the transparent sheet material and/or surfacetreatments thereto have a relatively low T_(G), melting temperature, orother heat tolerance parameter.

Referring specifically to FIG. 12 a, there is illustrated a sheet oftransparent material 304 having a window portion 312 defined thereupon.The window portion 312 has finished top and bottom surfaces 314 and 316(note that the 304 sheet appears bottom side up in FIGS. 12 a through 12c). A frame attachment area 1200 is defined on the sheet 304, the frameattachment area circumscribing the window portion 312. It will beappreciated in the embodiment illustrated in FIG. 12 that the frameattachment area 1200 need not follow the specific boundaries of thewindow area 312 (i.e., which in this case are circular) as long as theframe attachment area 1200 completely circumscribes the window portion.

It will be appreciated that, unless specifically noted otherwise, theinitial steps of obtaining a transparent sheet having a window portionwith finished top and bottom surfaces, preparing the seal-ring area ofthe sheet and metallizing the seal-ring area of the sheet aresubstantially identical to those described for the previous embodimentsand will not be described in detail again.

Referring now also to FIG. 13 a, there is illustrated a partialcross-sectional view to the edge of the sheet 304. In this example, thestep of preparing a frame attachment area 1200 on the sheet 304comprises an optional step of roughening the frame attachment area byroughening and/or grinding the surface from its original level (shown inbroken line) to produce a recessed area 1302. After the frame attachmentarea 1200 has been prepared, metal layers are deposited into the frameattachment area of the sheet using cold gas dynamic spray deposition. InFIG. 12 b, an initial metal layer 1202 has been applied into the frameattachment area 1200 using cold gas dynamic spray deposition.

Referring now also to FIG. 13 b, the cold gas dynamic spray nozzle 1304is shown depositing a stream of metal particles 1306 onto the frameattachment area 1200. The initial layer 1202 has now been overlaid witha secondary layer 1204 and the spray nozzle 1304 is shown as it beginsto deposit the final Kovar alloy layer 1206. Layer 1206 need not beKovar.

Referring now to FIG. 12 c, the completed cover assembly 1210 isillustrated including the integral frame/heat spreader 1212, which hasbeen built up from layer 1206 to a predetermined height, denoted byreference numeral 1308, above the finished surface of the sheet. In apreferred embodiment, the predetermined height 1308 of the built-upmetal frame above the frame attachment area 1200 is within the rangefrom about 5% to about 100% of the thickness denoted by referencenumeral 1310 of the sheet 304 beneath the frame attachment area. In theembodiment shown, the step of depositing metal using cold gas dynamicspray included depositing a layer of Kovar alloy onto the sheet tofabricate the built-up frame/heat spreader 1212. The use of cold gasdynamic spray deposition allows a tremendous range of thickness for thisKovar alloy layer, which thickness may be within the range from about2.54 microns to about 12,700 microns. It will, of course, be appreciatedthat the frame/heat spreader 1212 may be fabricated through thedeposition of materials other than Kovar alloy, depending upon thecharacteristics of the transparent sheet 304 and of the package base104, especially their respective CTEs.

The following examples, not to be considered limiting, are provided toillustrate the details of the metallic layers, denoted collectively byreference numeral 1207 for forming a frame/heat spreader compatible withhard glass transparent sheets and Kovar alloy or ceramic package bases.The deposition of materials other than Kovar alloy may be used as thefinal layer whenever Kovar Alloy is indicated as the final layer,depending upon the characteristics of the transparent sheet 304 and ofthe package base 104, especially their respective CTEs.

EXAMPLE 91

Min. Max. Layers Metal Deposition (microns) (microns) 1 Al cold gasspray 2.54 127 2 Cu cold gas spray 2.54 127 3 Ni cold gas spray 2.54 1274 Kovar Alloy cold gas spray 127 12,700

EXAMPLE 92

Min. Max. Layers Metal Deposition (microns) (microns) 1 Al cold gasspray 2.54 127 2 Ni cold gas spray 2.54 127 3 Kovar Alloy cold gas spray127 12,700

EXAMPLE 93

Min. Max. Layers Metal Deposition (microns) (microns) 1 Al cold gasspray 2.54 127 2 Kovar Alloy cold gas spray 127 12,700

EXAMPLE 94

Min. Max. Layers Metal Deposition (microns) (microns) 1 Kovar Alloy coldgas spray 127 12,700

EXAMPLE 95

Min. Max. Layers Metal Deposition (microns) (microns) 1 Zn cold gasspray 2.54 127 2 Ni cold gas spray 2.54 127 3 Kovar alloy cold gas spray127 12,700

EXAMPLE 96

Min. Max. Layers Metal Deposition (microns) (microns) 1 Zn cold gasspray 2.54 127 2 Kovar alloy cold gas spray 127 12,700

EXAMPLE 97

Min. Max. Layers Metal Deposition (microns) (microns) 1 Cr cold gasspray 2.54 127 2 Ni cold gas spray 2.54 127 3 Kovar alloy cold gas spray127 12,700

EXAMPLE 98

Min. Max. Layers Metal Deposition (microns) (microns) 1 Cr cold gasspray 2.54 127 2 Kovar alloy cold gas spray 127 12,700

EXAMPLE 99

Min. Max. Layers Metal Deposition (microns) (microns) 1 Al cold gasspray 2.54 127 2 Zn cold gas spray 2.54 127 3 Ni cold gas spray 2.54 1274 Kovar Alloy cold gas spray 127 12,700

EXAMPLE 100

Min. Max. Layers Metal Deposition (microns) (microns) 1 Ni cold gasspray 2.54 127 2 Kovar Alloy cold gas spray 127 12,700

EXAMPLE 101

Min. Max. Layers Metal Deposition (microns) (microns) 1 Sn or Sn—Bi coldgas spray 2.54 127 2 Zn cold gas spray 2.54 127 3 Ni cold gas spray 2.54127 4 Kovar Alloy cold gas spray 127 12,700

EXAMPLE 102

Min. Max. Layers Metal Deposition (microns) (microns) 1 Sn or Sn—Bi coldgas spray 2.54 127 2 Ni cold gas spray 2.54 127 3 Kovar Alloy cold gasspray 127 12,700

By way of further examples, not to be considered limiting, the followingcombinations are preferred for the metallic layers 1207 for forming aframe/heat spreader compatible with hard glass transparent sheets andKovar or other alloys or ceramic package bases. The deposition ofmaterials other than Kovar alloy may be used as the final layer wheneverKovar Alloy is indicated as the final layer, depending upon thecharacteristics of the transparent sheet 304 and of the package base104, especially their respective CTEs.

EXAMPLE 103

Min. Max. Layers Metal Deposition (microns) (microns) 1 Al cold gasspray 12.7 76.2 2 Cu cold gas spray 12.7 76.2 3 Ni cold gas spray 12.776.2 4 Kovar Alloy cold gas spray 635 2,540

EXAMPLE 104

Min. Max. Layers Metal Deposition (microns) (microns) 1 Al cold gasspray 12.7 76.2 2 Ni cold gas spray 12.7 76.2 3 Kovar Alloy cold gasspray 635 2,540

EXAMPLE 105

Min. Max. Layers Metal Deposition (microns) (microns) 1 Al cold gasspray 12.7 76.2 2 Kovar Alloy cold gas spray 635 2,540

EXAMPLE 106

Min. Max. Layers Metal Deposition (microns) (microns) 1 Kovar Alloy coldgas spray 635 2,540

EXAMPLE 107

Min. Max. Layers Metal Deposition (microns) (microns) 1 Zn cold gasspray 12.7 76.2 2 Ni cold gas spray 12.7 76.2 3 Kovar alloy cold gasspray 635 2,540

EXAMPLE 108

Min. Max. Layers Metal Deposition (microns) (microns) 1 Zn cold gasspray 12.7 76.2 2 Kovar alloy cold gas spray 635 2,540

EXAMPLE 109

Min. Max. Layers Metal Deposition (microns) (microns) 1 Cr cold gasspray 12.7 76.2 2 Ni cold gas spray 12.7 76.2 3 Kovar alloy cold gasspray 635 2,540

EXAMPLE 110

Min. Max. Layers Metal Deposition (microns) (microns) 1 Cr cold gasspray 12.7 76.2 2 Kovar alloy cold gas spray 635 2,540

EXAMPLE 111

Min. Max. Layers Metal Deposition (microns) (microns) 1 Al cold gasspray 12.7 76.2 2 Zn cold gas spray 12.7 76.2 3 Ni cold gas spray 12.776.2 4 Kovar Alloy cold gas spray 635 2,540

EXAMPLE 112

Min. Max. Layers Metal Deposition (microns) (microns) 1 Ni cold gasspray 12.7 76.2 2 Kovar Alloy cold gas spray 635 2,540

EXAMPLE 113

Min. Max. Layers Metal Deposition (microns) (microns) 1 Sn or Sn—Bi coldgas spray 12.7 76.2 2 Zn cold gas spray 12.7 76.2 3 Ni cold gas spray12.7 76.2 4 Kovar Alloy cold gas spray 635 2,540

EXAMPLE 114

Min. Max. Layers Metal Deposition (microns) (microns) 1 Sn or Sn—Bi coldgas spray 12.7 76.2 2 Ni cold gas spray 12.7 76.2 3 Kovar Alloy cold gasspray 635 2,540

After the deposition of the metal layers using the cold gas dynamicspray deposition, it may be necessary to grind or shape the top surfaceof the built-up frame 1212 to a predetermined flatness before performingadditional steps to ensure that a good contact will be made in laterbonding. Another process that may be used, either alone or incombination with shaping the top surface of the built-up frame, is thedepositing of additional metal layers onto the built-up frame/heatspreader 1212 using solution bath plating. The most common reason forsuch plated layers is to promote a good bonding when the frame/heatspreader is adjoined to the package base 104. In a preferred embodiment,the additional metallic layers applied to the built-up frame 1212include a layer of nickel directly over the cold gas dynamic spraydeposited metal having a thickness within the range of about 0.002microns to about 25 microns and, in some instances, then solution bathplating a layer of gold over the nickel layer until the gold layer has athickness within the range from about 0.0508 microns to about 0.508microns.

Referring now to FIG. 14, there is illustrated a block diagram of thealternative embodiment utilizing cold gas dynamic spray deposition. Itwill be appreciated that, unless specifically noted otherwise, theinitial steps of obtaining a transparent sheet having finished surfaces,applying surface treatments to the sheet, cleaning, roughening orotherwise preparing the frame attachment area of the sheet aresubstantially identical to those described for the previous embodimentsand will not be described in detail again. For example, block 1402 ofFIG. 14 represents the step of obtaining a sheet of transparent materialhaving finished surfaces and corresponds directly with block 902, andwith the description of suitable transparent materials. Similarly,except as noted, blocks 1404, 1406 and 1408 of FIG. 14 corresponddirectly with blocks 904, 906 and 908, respectively, of FIG. 9 and withthe previous descriptions of the steps and sub-steps provided herein.Thus, it will be understood that all of the options described forperforming the various steps and sub-steps represented by the blocks902-908 in the previous (i.e., prefabricated frame) embodiments areapplicable to the blocks 1402-1408 in the current (i.e., cold spray)embodiment.

The next step of the process is to use cold gas dynamic spray depositionto deposit frame/heat spreader metal onto any previously deposited metallayers in the frame attachment area 1200. This step is represented byblock 1410. As previously described in connection with FIGS. 13 b and 13c, the high velocity particles 1306 from the gas nozzle 1304 form a newlayer on the previous metallic layers, and by directing the cold sprayjet across the frame attachment area 1200 repeatedly, the new materialcan become a continuous metallic layer around the entire periphery ofthe frame attachment area, i.e., it will circumscribe the window portion312 of the transparent sheet 304. Where the material of the package base104 (to which the cover assembly 1210 will eventually be joined) isKovar alloy or appropriately metallized alumina, Kovar alloy ispreferred for the material 1206 to be cold sprayed to form the integralframe. In other cases, a heat spreader material should be selected whichhas a CTE that is closely matched to the CTE of the package base 104. Ofcourse, that material must also be compatible with the cold gas dynamicspray process.

The cold spraying of the powdered heat spreader material is continueduntil the new layer 1206 reaches the thickness required to serve as aheat spreader/integral frame. This would represent the end of theprocess represented by block 1410. For some applications, the built-upheat spreader/frame 1212 is now complete and ready for use. For otherapplications, however, performing further finishing operations on theheat spreader/frame 1212 may be desirable.

For example, it is known that significant residual stresses may beencountered in metal structures deposited using cold-gas dynamic spraytechnology as a result of the mechanics of the spray process. Thesestresses may make the resulting structure prone to dimensional changes,cracking or other stress-related problems during later use. Annealing bycontrolled heating and cooling is known to reduce or eliminate residualstresses. Thus, in some applications, the integral heat spreader/frame1212 is annealed following its deposition on the sheet 304. Thisoptional step is represented by block 1411 in FIG. 14. In someembodiments, the annealing step 1411 may include the annealing of thetotality of the sprayed-on metals and alloys constituting the heatspreader/frame 1212. In other embodiments, however, the annealing step1411 includes annealing only the outermost portions of the integralbuilt-up heat spreader/frame 1212, while the inner layers are leftunannealed.

It will be appreciated that there are flatness requirements for thesealing surface at the “top” of the heat spreader (which is actuallyprojecting from the bottom surface 316 of the sheet). If these flatnessrequirements are not met via the application of the heat spreadermaterial by the cold spray process, it will be necessary to flatten thesealing surface at the next step of the process. This step isrepresented by block 1412 in FIG. 14. There are a number of options forachieving the required surface flatness. First, it is possible to removesurface material from the heat spreader to achieve the requiredflatness. This may be accomplished by conventional surface grinding, byother traditional mechanical means, or it may be accomplished by thelaser removal of high spots. Where material removal is used, care mustbe taken to avoid damaging the finished window surfaces 314 and 316during the material removal operations. Special fixturing and/or maskingof the window portion 312 may be required. Alternatively, if the coldspray deposited heat spreader 1212 is ductile enough, the surface may beflattened using a press operation, i.e., pressing the frame against aflat pattern or by employing a rolling operation. This would reduce thehandling precautions as compared to using a surface grinder or laseroperations.

Finally, as previously described, in some embodiments additional metallayers are plated onto the integral frame/heat spreader 1212. Theseoptional plating operations, such as solution bath plating layers ofnickel and gold onto a Kovar alloy frame, are represented by block 1414in FIG. 14. In the embodiment shown in FIG. 14, the optional platingoperation 1414 is performed after the optional flattening operation1412, which in turn is performed after the optional annealing operation1411. While such order is preferred, it will be appreciated that inother embodiments the order of the optional finishing steps 1411, 1412and 1414 may be rearranged. The primary consideration for the orderingof these finishing steps is whether later steps will damage the resultsof earlier steps. For example, it would be impractical to performplating step 1414 before the flattening step 1412 if the flattening wasto be carried out by grinding, while it might be acceptable if theflattening was to be carried out by pressing.

Referring now to FIGS. 15 a and 15 b, there is illustrated a method formanufacturing multiple cover assemblies simultaneously in accordancewith another embodiment of the current invention. Shown in FIG. 15 a isan exploded view of a multi-unit assembly that can be subdivided afterfabrication to produce individual cover assemblies. The multi-unitassembly 1500 includes a frame 1502 and a sheet 1504 of a transparentmaterial. The frame 1502 has sidewalls 1506 defining a plurality offrame apertures 1508 therethrough. Each frame aperture 1508 iscircumscribed by a continuous sidewall section having a frame seal-ringarea 1510 (denoted by cross-hatching). Each frame seal-ring area 1510has a metallic surface, which may result from the inherent material ofthe frame 1502 or it may result from metal layers that have been appliedto the surface of the frame. In some embodiments, the frame 1502includes reduced cross-sectional thickness areas 1509 formed on theframe sidewalls 1506 between adjacent frame apertures 1508. FIG. 15 bshows the bottom side of the frame 1502, to better illustrate thereduced cross-sectional thickness areas 1509 formed between eachaperture 1508. Also illustrated is the base seal-ring area 1520 (denotedby cross-hatching) which surrounds each aperture 1508 to allow joiningto the package bases 104.

Further regarding the multi-aperture frames illustrated in FIGS. 15 aand 15 b, it will be understood that the frame 1502 can be attached asshown, with the open ends of the V-shaped notches facing away from thesheet, or alternatively, with the open ends of the V-shaped notchesfacing toward the sheet.

Except for the details just described, the multiple-aperture frame 1502of this embodiment shares material, fabrication and design details withthe single aperture frame 302 previously described. In this regard, apreferred embodiment of the frame 1502 is primarily formed of Kovaralloy or similar materials and more preferably, will have a Kovar alloycore with a surface layer of gold overlaying an intermediate layer ofnickel as previously described.

The transparent sheet 1504 for the multi-unit assembly can be formedfrom any type of transparent material as previously discussed for sheet304. In this embodiment, however, the sheet 1504 has a plurality ofwindow portions 1512 defined thereupon, with each window portion havingfinished top and bottom surface 1514 and 1516, respectively. A pluralityof sheet seal-ring areas 1518 are denoted by cross-hatching surroundingeach window portion in FIG. 15 a. With respect to the material of thesheet 1504, with respect to the finished configuration of the top andbottom surfaces 1514 and 1516, respectively, of each window portion1512, with respect to surface treatments, and/or coatings, the sheet1504 is substantially identical to the single window portion sheet 304previously discussed.

The next step of the process of manufacturing the multi-unit assembly1500 is to prepare the sheet seal-ring areas 1518 for metallization. Asnoted earlier, each sheet seal-ring area 1518 circumscribes a windowportion of the sheet 1504. The sheet seal-ring areas 1518 typically havea configuration which closely matches the configuration of the frameseal-ring areas 1510 to which they will eventually be joined. It will beappreciated, however, that in some cases other considerations willaffect the configuration of the frame grid, e.g., when electricalresistance heating is used to produce bonding, then the seal-ring areas1518 must be connected to form the appropriate circuits. The steps ofpreparing the sheet seal-ring areas 1518 for metallization issubstantially identical to the steps and options presented duringdiscussion of preparing the frame seal-ring area 310 on the singleaperture frame 302. Thus, at a minimum, preparing the sheet seal-ringarea 1518 typically involves a thorough (e.g., plasma, solvent ordetergent) cleaning to remove any contaminants from the surfaces andtypically also involves roughening the seal-ring area by chemicaletching, laser ablating, mechanical grinding or sandblasting this area.

The step of metallizing the prepared sheet seal-ring areas 1510 of thesheet 1502 are substantially identical to the steps described formetallizing the frame seal-ring area 310 on the single aperture frame302. For example, the metal layers shown in Examples 1 through 120 canbe used in connection with thermal compression bonding, for solderingwhere the solder material is plated onto the sheet as a final metalliclayer, and can be used in connection with soldering in combination witha separate gold-tin of solder preform and also for soldering inconnection with solders deposited or formed using inkjet technology.

The next step of the process is to position the frame 1502 against thesheet 1504 (it being understood that solder preforms or solder layerswould be interposed between the frame and the sheet if braze solderingis used to join the frame 1502 to the sheet 1504) such that each of thewindow portions 1512 overlays one of the frame apertures 1508, and thatfor each such window portion/frame aperture combination, at least aportion of the associated frame seal-ring area 1510 and at least aportion of the associated sheet seal-ring area 1518 contact one anotheralong a continuous junction region that circumscribes the associatedwindow portion. This operation is generally analogous to the steps ofpositioning the frame against the sheet in the single apertureembodiment previously described. If diffusion bonding is used to jointhe frame 1502 to the sheet 1504, an interlayer or innerlayer betweenthe frame 1502 to the sheet 1504 may or may not be employed.

Referring now to FIG. 16 a, there is illustrated the positioning of amulti-window sheet 1504 (in this case having window portions 1512 withcontoured surfaces) against a multi-aperture frame 1502 using complianttooling in accordance with another embodiment. The compliant toolingincludes a compliant element 1650 and upper and lower support plates1652, 1654, respectively. The support plates 1652 and 1654 receivecompressive force, denoted by arrows 1656, at discrete locations fromtooling fixtures (not shown). The compliant member 1650 is positionedbetween one of the support plates and the cover assembly pre-fab (i.e.,frame 1502 and sheet 1504). The compliant member 1650 yields elasticallywhen a force is applied, and therefore can conform to irregular surfaces(such as the sheet 1504) while at the same time applying a distributedforce against the irregular surface to insure that the required contactpressure is achieved all along the frame/sheet junction. Such complianttooling can also be used to press a sheet or frame against the othermember when the two members are not completely flat, taking advantage ofthe inherent flexibility (even if small) present in all materials. Inthe illustrated example, the compliant member 1650 is formed from asolid block of an elastomer material, e.g., rubber, however in otherembodiments the compliant member may also be fabricated from discreteelements, e.g., springs. The compliant material must be able towithstand the elevated temperatures experienced during the bondingoperation.

The next step of the process is heating all of the junction regionsuntil a metal-to-metal joint is formed between the frame 1502 and thesheet 1504 all along each junction region, thus creating the multi-unitassembly 1500 having a hermetic frame/sheet seal circumscribing eachwindow portion 1512. If diffusion bonding is used to join the frame 1502and the sheet 1504, the bond could be between the outermost metal layerof the frame and the non-metallized sheet 1504. It will be appreciatedthat any of the heating technologies previously described for joiningthe single aperture frame 302 to the single sheet 304 are applicable tojoining the multi-aperture frame 1502 to the corresponding multi-windowsheet 1504.

Referring now to FIG. 16 b, the final step of the current process is todivide the multi-unit assembly 1500 along each junction region that iscommon between two window portions 1512 taking care to preserve andmaintain the hermetic seal circumscribing each window portion. Aplurality of individual cover assemblies are thereby produced. FIG. 16b, illustrates a side view of a multi-unit assembly 1500 following thehermetic bonding of the sheet 1504 to the frame 1502. Where the frame1502 includes reduced cross-sectional thickness areas 1509, the step ofdividing the multi-unit assembly may include scoring the frame along theback side of the reduced cross-sectional thickness area at the positionindicated by arrow 1602, preferably breaking through or substantiallyweakening the remaining frame material below area 1509, and alsosimultaneously scoring the sheet 1504 along a line vertically adjacentto area 1509, i.e., at the point indicated by arrow 1604, followed byflexing the assembly 1500, e.g., in the direction indicated by arrows1606 such that a fracture will propagate away from the score along line1608, thereby separating the assembly into two pieces. This procedurecan be repeated along each area of reduced cross-sectional thickness1509 until the multi-unit assembly 1500 has been completely subdividedinto single aperture cover assemblies that are substantially identicalto those produced by the earlier method described herein. In otherembodiments, instead of using the score-and-break method, the coverassemblies may be cut apart, preferably from the frame side along thepath indicated by arrow 1602 (i.e., between the window portions 1512),using mechanical cutting, dicing wheel, laser, water jet or otherparting technology.

Referring now to FIGS. 17 a and 17 b, there is illustrated yet anothermethod for simultaneously manufacturing multiple cover assemblies. Thismethod expands upon the cold gas dynamic spray technique used to buildan integral frame/heat spreader directly upon the transparent sheetmaterial as previously illustrated in connection with FIGS. 12 a through12 c and FIGS. 13 a through 13 c. As shown in FIG. 17 a, the processstarts with a sheet of nonmetallic transparent material 1704 having aplurality of window portions 1712 defined thereupon, each window portionhaving finished top and bottom surfaces 1714 and 1716, respectively. Theproperties and characteristics of the transparent sheet 1704 aresubstantially identical to those in the embodiments previouslydiscussed. The next step of the process involves preparing a pluralityof frame attachment areas 1720 (denoted by the path of the broken linesurrounding each window portion 1712), each frame attachment area 1720circumscribing one of the window portions 1712. As in previousembodiments, the step of preparing the frame attachment areas maycomprise cleaning, roughening, grinding or otherwise modifying the frameattachment areas in preparation for metallization.

The next step in this process is metallizing the prepared frameattachment areas on the sheet, i.e., this metallization may be performedusing a cold gas dynamic spray technology or where the layers arerelatively thin, using a CVD, physical vapor deposition or otherconventional metal deposition techniques. It will be appreciated thatthe primary purpose of this step is to apply metal layers necessary toobtain good adhesion to the transparent sheet 1704 and/or to meet themetallurgical requirements for corrosion prevention, etc.

Referring now to FIG. 17 b, the next step of the process is depositingmetal onto the prepared/metallized frame attachment areas of the sheet1704 using cold gas dynamic spray deposition techniques until a built-upmetal frame 1722 is formed upon the sheet having a seal-ring area 1726that is a predetermined vertical thickness above the frame attachmentareas, thus creating a multi-unit assembly having an inherent hermeticseal between the frame 1722 and the sheet 1704 circumscribing eachwindow portion 1712. In some embodiments, reduced cross-sectionalthickness areas 1724 are formed by selectively depositing the metalduring the cold spray deposition. In other embodiments, the reducedcross-sectional area sections 1724 may be formed following deposition ofthe frame/heat spreader 1722 through the use of grinding, cutting orother mechanical techniques such as laser ablation and water jet. Inaddition, the reduced cross-sectional area sections 1724 may be formedfollowing deposition of the frame/heat spreader 1722 through the use ofphoto-chemical machining (PCM).

The next step of the process, while not required is strongly preferred,is to flatten, if necessary, the seal-ring area 1726 of the sprayed-onframe 1722 to meet the flatness requirements for joining it to thepackage base 104. This flattening can be accomplished by mechanicalmeans, e.g., grinding, lapping, polishing, etc., or by other techniquessuch as laser ablation.

The next step of the process, which, while not required, is stronglypreferred, is to add additional metallic layers, e.g., a nickel layerand preferably also a gold layer, to the seal-ring area 1726 of thesprayed-on frame 1722 to facilitate welding the cover assembly to thepackage base 104. These metallic layers are preferably added using asolution bath plating process, e.g., solution bath plating, althoughother techniques may be used.

The next step of the process is dividing the multi-unit assembly 1700along each frame wall section common between two window portions 1712while, at the same time, preserving and maintaining the hermetic sealcircumscribing each window portion. After dividing the multi-unit 1700,a plurality of single aperture cover assemblies 1728 (shown in brokenline) will be produced, each one being substantially identical to thesingle aperture cover assemblies produced using the method described inFIGS. 12 a through 12 c and FIGS. 13 a through 13 c. All of the options,characteristics and techniques described for use in the single unitcover assembly produced using cold gas dynamic spray technology areapplicable to this embodiment. It will be appreciated that certainoperations for example, the flattening of the frame and the plating ofthe frame with additional metallic layers, may be performed on themulti-unit assembly 1700, prior to separation of the individual units,or on the individual units after separation.

As previously described, heating the junction region between themetallized seal-ring area of the transparent sheet and the seal-ringarea of the frame is required for forming the hermetic sealtherebetween. Also as previously described, this heating may beaccomplished using a furnace, oven, or various electrical heatingtechniques, including electrical resistance heating (ERH). Referring nowto FIGS. 18 a-18 c, there is illustrated methods of utilizing electricresistance heating to manufacture multiple cover assembliessimultaneously.

Referring first to FIG. 18 a, there is illustrated a transparent sheet1804 having a plurality of seal-ring areas 1818 laid out in arectangular arrangement around a plurality of window portions 1812.These seal-ring areas 1818 have been first prepared, and then metallizedwith one or more metal or metal alloy layers, as previously describedherein. The transparent sheet 1804 further includes an electrode portion1830 that has been metallized, but does not circumscribe any windowportions 1812. This electrode portion is electrically connected to themetallized seal-ring areas 1818 of the sheet. One or more electrode pads1832 may be provided on the electrode portion 1830 to receive electricalenergy from electrodes during the subsequent ERH procedure.

Referring now to FIG. 18 b, there is illustrated a frame 1802 having aplurality of sidewalls 1806 laid out in a rectangular arrangement arounda plurality of frame apertures 1808. The apertures 1808 are disposed soas to correspond with the positions of the window portions 1812 of thesheet 1804, and the sidewalls 1806 are disposed so that frame seal-ringareas 1810 (located thereupon) correspond with the positions of thesheet seal-ring areas 1818 of the sheet. The frame is metallic ormetallized in order to facilitate joining as previously describedherein. The frame 1802 further includes an electrode portion 1834 thatdoes not circumscribe any frame apertures 1808. This frame electrodeportion 1834 is positioned so as not to correspond to the position ofthe sheet electrode portion 1830, and preferably is disposed on anopposing side of the sheet-window/frame-grid assembly (i.e., when thesheet is assembled against the frame). The frame electrode portion 1834is electrically connected to the metallized frame seal-ring areas 1810.One or more electrode pads 1836 may be provided on the electrode portion1834 to receive electrical energy from electrodes during the subsequentERH procedure.

Referring now to FIG. 18 c, the sheet 1804 is shown positioned againstthe frame 1802 in preparation for heating to produce the hermetic sealtherebetween. If applicable, solder or a solder preform has beenpositioned therebetween as previously described. It will be appreciatedthat when the transparent sheet 1804 is brought against the frame 1802,the metallized seal-ring areas 1818 on the lower surface of the sheetwill be in electrical contact with the metallized seal-ring areas 1810on the upper surface of the frame. However, the sheet electrode portion1830 and the frame electrode portion 1834 will not be in direct contactwith one another, but instead will be electrically connected onlythrough the metallized seal-ring areas 1818 and 1810 to which they are,respectively, electrically connected. When an electrical potential isapplied from electrode pads 1832 to electrode pads 1836 (denoted by the“+” and “−” symbols adjacent to the electrodes), electrical currentflows through the junction region of the entire sheet-window/frame-gridassembly. This current flow produces electrical resistance heating (ERH)due to the resistance inherent in the metallic layers. In someembodiments, this electrical resistance heating may be sufficient tosupply the necessary heat, in and of itself, to result in TC bonding,soldering, or other hermetic seal formation between the sheet 1804 andthe frame 1802 in order to form a multi-unit assembly. In otherembodiments, however, electrical resistance heating may be combined withother heating forms such as furnace or oven pre-heating in order tosupply the necessary heat required for bonding to form the multi-unitassembly.

After bonding the sheet 1804 to the frame 1802 to form the multi-unitassembly, the sheet electrode portion 1830 and the frame electrodeportion 1834 can be cut away and discarded, having served their functionof providing electrical access for external electrodes (or otherelectrical supply members) to the metallized seal-ring areas of thesheet and frame, respectively. The removal of these “sacrificial”electrode portions 1830 and 1834 may occur before or during the “dicing”process step, i.e., the separating of the multi-unit assembly intoindividual cover assemblies. It will be appreciated that any of thetechnologies previously described herein for separating a multi-unitassembly into individual cover assemblies can be used for the dicingstep of separating a multi-unit assembly fabricated using ERH heating.

Where ERH is to be used for manufacturing multiple cover assembliessimultaneously, the configuration of the sheet-window/frame-grid arrayand/or the placement of the electrodes portions within thesheet-window/frame-grid array may be selected to modify the flow ofcurrent through the junction region during heating. The primary type ofmodification is to even the flow of current through the various portionsof the sheet-window/frame-grid during heating to produce more eventemperatures, i.e., to avoid “hot spots” or “cold spots.”

Referring now to FIGS. 19 a-19 f, there are illustrated varioussheet-window/frame-grid configurations adapted for producing more eventemperatures during ERH. In each of FIGS. 19 a-19 f, there is shown asheet-window/frame-grid array 1900 comprising a prepared, metallizedtransparent sheet 1904 overlying a prepared, metallic/metallized frame1902. The window portions of the sheet 1904 directly overlie the frameapertures of the frame 1902, and the metallized seal-ring areas of thesheet directly overlie the seal-ring areas of the frame (it will beappreciated that metallized portions of the sheet 1904 and the frame1902 appear coincident in these figures). Metallized electrode portionsformed on the transparent sheet 1904 are denoted by reference letters A,B, C and D. These electrode portions A, B, C and D are electricallyconnected to the adjoining sheet seal-ring areas of the sheet, but areelectrically insulated from one another by non-metallized areas 1906 ofthe sheet. An external electrode is applied to the top of themetallic/metallized frame (on the side opposite from the sheet) acrossthe area denoted by reference letter E. For bonding or soldering,electrical power is applied at the electrodes, e.g., one line toelectrodes A, B, C and D simultaneously, and the other line to electrodeE, or alternatively, one line in sequence to each of electrode A, B, Cand D, and the other line to electrode E. It will be appreciated thatmany other combinations of electrode powering are within the scope ofthe invention.

Referring to FIG. 19 f, this embodiment illustrates asheet-window/frame-grid 1900 having a “shingle” configuration, i.e.,where the seal-ring areas between the window portions/frame apertures donot form continuous straight lines across the assembly array.Shingle-arrangement frame assemblies are more labor-intensive toseparate using scribe-and-break or cutting procedures. Separating suchassemblies requires that each row first be separated from the overallgrid, and then that individual cover assemblies be separated from therow by separate scribe-and-break or cutting operations. Nevertheless,use of shingle-arrangement assemblies may have benefits relating toheating using ERH techniques.

It will be understood that a metal frame such as 1802 or 1902, which maycontain one or more added layers on its exterior, including but notlimited to metal or metal alloy layers, may be diffusion bonded to anon-metallized sheet using ERH techniques to apply heat to the frame.The amount of temperature rise throughout the thickness of thenon-metallized sheet will depend on the intensity and duration of theapplication of the electrical power (voltage and amperage) to the frame,as well as other factors. An innerlayer or interlayer material may beemployed between the frame and the sheet during the diffusion bondingprocess, as discussed previously.

It will further be appreciated that the terms “thermal compressionbonding” (and its abbreviation “TC bonding”) and “diffusion bonding” areused interchangeably throughout this application. The term “diffusionbonding” is preferred by metallurgists while the term “thermalcompression bonding” is preferred in many industries (e.g.,semiconductor manufacturing) to avoid possible confusion with othertypes of “diffusion” processes used for creating semiconductor devices.Regardless of which term is used, as previously discussed, diffusionbonding refers to the family of bonding methods using heat, pressure,specific positive or negative pressure atmospheres and time alone tocreate a bond between mating surfaces at a temperature below the normalfusing temperature of either mating surface. In other words, neithermating surface is intentionally melted, and no melted filler material isadded, nor any chemical adhesives used.

As previously described, diffusion bonding utilizes a combination ofelevated heat and pressure to hermetically bond two surfaces togetherwithout first causing one or both of the adjoining surfaces to melt (asis the case with conventional soldering, brazing and welding processes).When making optical cover assemblies, wafer level assemblies or othertemperature-sensitive articles, it is almost always required that thebonding temperatures remain below some upper limit. For example, inoptical cover assemblies, the bonding temperature should be below theT_(G) and the softening temperature, T_(S), of the sheet material so asnot to affect the pre-existing optical characteristics of the sheet. Asanother example, in wafer level assemblies, the bonding temperatureshould be below the upper temperature limit for the embedded microdevice and/or its operating atmosphere (i.e., the gas environment insidethe sealed package). However, the specific temperature and pressureparameters required to produce a hermetic diffusion bond can vary widelydepending upon the nature and composition of the two mating surfacesbeing joined. Therefore, it is possible that some combinations oftransparent sheet material (e.g., glass) and frame material (e.g.,metals or metallized non-metals), or some combinations of framematerials and substrate materials (e.g., silicon, alumina or metals),will have a diffusion bonding temperature that exceeds the T_(G) and/orthe T_(S) of the sheet material, or that exceeds some other temperaturelimit. In such cases, it might appear that diffusion bonding isunsuitable for use in hermetically joining the components together ifthe temperature limits are to be followed. In fact, however, it has beendiscovered that the use of “interlayers,” i.e., intermediate layers ofspecially selected material, placed between the sheet material and theframe, or between the frame material and the substrate material, cancause hermetic diffusion bonding to take place at a substantially lowertemperature than if the same sheet material was bonded directly to thesame frame material, or if the same frame material was bonded directlyto the same substrate material. Note that the terms “interlayers” and“innerlayers” are used interchangeably throughout this application, asboth terms may be encountered in the art for the same thing.

A properly matched interlayer improves the strength and hermeticity(i.e., gas tightness or vacuum tightness) of a diffusion bond. Further,it may promote the formation of compatible joints, produce a monolithicbond at lower bonding temperatures, reduce internal stresses within thebond zone, and prevent the formation of extremely stable oxides thatinterfere with diffusion, especially on the surface of Al, Ti andprecipitation-hardened alloys. The interlayer is believed to diffuseinto the parent material, thereby raising the melting point of the jointas a whole. Depending upon the materials to be joined by diffusionbonding, the interlayer material could be composed of a metal, a metalalloy, a glass material, a solder glass material including solder glassin tape or sheet form, or other materials. In the diffusion bonding ofBT5-1 Ti alloy to Armco iron, an interlayer of molybdenum foil 0.3 mmthick has been used. Reliable glass-to-glass and glass-to-metal bondsare achieved with metal interlayers such as Al, Cu, Kovar, Niobium andTi in the form of foil, usually not over 0.2 mm thick. The interlayersare typically formed into thin preforms shaped like the seal ring areaof the mating surfaces to be joined.

It is important to distinguish the use of diffusion bonding interlayersfrom the use of conventional solder preforms and other processespreviously disclosed. For purposes of this application, an interlayer isa material used between sealing surfaces to promote the diffusionbonding of the surfaces by allowing the respective mating surfaces todiffusion bond to the interlayer rather than directly to one another.For example, with the proper interlayer material, the diffusion bondingtemperature for the joint between the sheet material and interlayermaterial, and for the joint between the interlayer material and theframe material, may be substantially below the diffusion bondingtemperature of a joint formed directly between the sheet material andthe frame material. Thus, use of the interlayer allows diffusion bondingof the sheet to the frame at a temperature that is substantially belowthe diffusion bonding temperature that would be necessary for bondingthat sheet material and that frame material directly. The hermetic jointis still formed by the diffusion bonding process, i.e., none of thematerials involved (the sheet material, the interlayer material nor theframe material) melts during the bonding process. This distinguishesdiffusion bonding using interlayers from other processes such as the useof solder preforms in which the solder material actually melts to formthe bond between the materials being joined. It is possible to usematerials conventionally used for solders, for example, Au—Sn solderpreforms, as interlayers for diffusion bonding. However, when used asinterlayers they are used for their diffusion bonding properties and notas conventional solders (in which they melt).

The use of interlayers in the production of window assemblies or otherpackaging may provide additional advantages over and above their use aspromoting diffusion bonding. These advantages include interlayers thatserve as activators for the mating surfaces. Sometimes the interlayermaterials will have a higher ductility in comparison to the basematerials. The interlayers may also compensate for stresses that arisewhen the seal involves materials having different coefficients ofthermal expansion or other thermal expansion properties. The interlayersmay also accelerate the mass transfer or chemical reaction between thelayers. Finally, the interlayers may serve as buffers to prevent theformation of undesirable chemical or metallic phases in the jointbetween components.

Referring now to FIGS. 20 a and 20 b, there is illustrated a windowcover assembly including interlayers to promote joining by diffusionbonding. In this embodiment, the window assembly 2050 includes atransparent glass sheet 2052, an interlayer 2054 and a metal or metalalloy base 2056. The base 2056 includes a built-up seal ring area 2058and a flange 2060 that facilitates the subsequent electric resistanceseam welding of the finished window assembly to a package base or otherhigher level portion of the final component. The interlayer 2054 in thisembodiment takes the form of a metallic preform that has theconfiguration selected to match the seal ring area 2058 of the frame. Toform the hermetic window assembly, the sheet 2052, interlayer 2054 andframe 2056 are placed in a fixture (i.e., tooling) or mechanicalapparatus (not shown) which can provide the required predeterminedbonding pressure between the seal ring areas of the respectivecomponents. In some cases, the fixture may serve only to align thecomponents during bonding, while the elevated bonding pressure isapplied from a mechanical apparatus such as a ram. In other cases,however, the fixture may be designed to constrain the expansion of thestacked components during heating (i.e., along the stacking axis),whereby the thermal expansion of the assembly components toward thefixture, and of the fixture itself toward the components, will“self-generate” some or all of the necessary bonding pressures betweenthe components as the temperature increases.

Referring now to FIGS. 20 e and 20 f, an example of a “self-compressing”fixture assembly is shown. As best seen in FIG. 20 e, the fixture 2085includes an upper fixture member 2086 and a lower fixture member 2087that together define a cavity 2088 for receiving the window assemblycomponents to be bonded. Clamps 2089 are provided which constrain theoutward movement of the fixture members 2086 and 2087 in the axialdirection (denoted by arrow 2090). Generally, the CTE of the materialforming the clamps 2089 will be lower than the CTE of the materialforming the fixture members 2086 and 2087. FIG. 20 f shows thecomponents for the window assembly 2070 (FIGS. 20 c and 20 d) loadedinto the cavity 2088 of the fixture 2085 in preparation for bonding.Note that while the fixture members 2086 and 2087 are in contact withthe upper and lower surfaces of the window components, a small gap 2097is left between the fixture members themselves to allow the members toexpand axially toward one another when heated (since they areconstrained by the clamps). Also note that a small gap 2098 is generallyleft between the lateral sides of the window assembly components and thefixture members 2086 and 2087 to minimize the lateral force exerted onthe components by the fixture members during heating. When the fixture2085 is heated, the inner surfaces (i.e., facing the cavity 2088) of thefixture members 2086 and 2087 will expand (due to thermal expansion)axially toward one another against the window components, and the windowcomponents will expand outward against the fixture. These thermalexpansions can press the window components against one another withgreat force in the axial direction to facilitate diffusion bonding. Itwill be appreciated that thermal expansion of the fixture members 2086and 2087 will also occur in the lateral direction (denoted by arrow2091). While this lateral expansion is not generally desired, in mostcases is will not present an obstacle to the use of self-compressingfixtures.

Referring now to FIG. 20 g, there is illustrated an alternativeself-compressing fixture adapted to enhance thermal expansion (and hencecompression) in the axial direction 2090 without causing excessivethermal expansion in the lateral direction 2091. As with the previousexample, alternative fixture 2092 includes an upper fixture member 2086and a lower fixture member 2087 defining a cavity 2088 for receiving thewindow assembly components to be bonded, and clamps 2089 (only one ofwhich is shown for purposes of illustration) which constrain the outwardmovement of the fixture members in the axial direction 2090. Also as inthe previous embodiment, a first small gap 2097 is present between thefixture members 2086 and 2087 themselves, and a second small gap 2098 ispresent between the lateral sides of the window components and thefixture members. Unlike the previous embodiment, however, each fixturemember 2086 and 2087 of the alternative fixture 2092 comprises twosub-members, namely, first sub-members 2093 and 2094, respectively,adapted to bear primarily axially against the window assembly components(not shown), and second sub-members 2095 and 2096, respectively, adaptedto hold and align the window assembly components in the cavity. Byselecting a material for the first sub-members 2093 and 2094 having ahigh CTE, axial expansion (and hence compression) during heating will becorrespondingly high. However, lateral expansion and relative lateralmovement between the second sub-members 2095 and 2096 and the windowcomponents can be minimized by selecting a different material for thesecond sub-members, namely, a material having a lower CTE (i.e., lowerthan the CTE for the first sub-members). Preferably, the CTE of thesecond sub-members 2095 and 2096 will be close to the CTE for theadjacent window components.

Referring again to FIGS. 20 a and 20 b, the assembled (but not yetbonded) components of the window assembly 2050 are then heated until thediffusion bonding pressure/temperature conditions are reached, and theseconditions are maintained until a first diffusion bond is formed betweenthe sheet 2052 and the interlayer 2054, and a second diffusion bond isformed between the interlayer 2054 and the seal ring area 2058 of theframe 2056. It will be understood that the first bond between the sheetand the interlayer may actually occur before, after or simultaneouslywith, the second bond between the interlayer and the frame. Aspreviously explained, it will also be understood that the order ofapplying heat and pressure to form the diffusion bond is not believed tobe significant, i.e., in other words whether the pre-determined pressureis applied, and then the heat is applied or whether the heat is appliedand then the predetermined pressure is applied, or whether both heat andpressure are increased simultaneously is not believed to be significant,rather the diffusion bonding will occur when the preselected pressureand temperature are present in the bond region for a sufficient amountof time. After the diffusion bonds are formed, the sheet 2052 will behermetically bonded to the frame 2056 to form a completed windowassembly 2050 as shown in FIG. 20 b.

In further embodiments of the current invention, it has been discoveredthat clean, i.e., unmetallized, glass windows may be directly bonded toframes of Kovar or other metallic materials using diffusion bonding.This is in addition to the diffusion bonding of metallized glass windowsto Kovar frames as previously described. Optionally, the directdiffusion bonding of unmetallized glass windows to metallic frames maybe enhanced through the use of certain compounds, e.g.,molybdenum-manganese, on the frames. Whether the glass is metallized orunmetallized, the diffusion bonding is most commonly performed in avacuum, however, it may be performed in various other atmospheres. Theuse of oxidizing atmospheres is typically not required, however, as anyresulting oxides tend to be dispersed by pressures encountered in thebonding operation. In still other embodiments, of the invention,diffusion bonding can be used for joining frames made of Kovar and othermetallic materials directly to sheets or wafers of semiconductormaterials including silicon and gallium arsenide (GaAs).

Since successful diffusion bonding requires the mating surfaces beingbonded to be brought into intimate contact with one another, the surfacefinish characteristics of the mating surfaces may be importantparameters of the invention. It is believed that the following matingsurface parameters will allow successful diffusion bonding between themating surfaces of Kovar frames and thin sheet materials including, butnot limited to, Kovar to metallized glass, Kovar to clean (i.e.,unmetallized) glass, Kovar to metallized silicon, Kovar to clean (i.e.,unmetallized) silicon, Kovar to metallized gallium arsenide (GaAs) andKovar to clean (i.e., unmetallized) GaAs: Parallelism of sheet material(i.e., uniformity of thickness) within the range of about 12.7 microns;Surface flatness (i.e., deviation in height per unit length when placedon ideal flat surface) within range from 5 mils/inch to about 10mils/inch; Surface roughness not more than about 16 micro-inches (0.4064microns). These surface parameters can also be used for diffusionbonding of Kovar directly to Kovar, e.g., to manufacture built-upmetallic frames.

The temperature parameters for diffusion bonding between the matingsurfaces of Kovar frames and the thin sheet materials described aboveare believed to be within the range from about 40% to about 70% of theabsolute melting temperature, in degrees Kelvin, of the parent materialhaving the lower melting temperature. When diffusion bonding is used forbonding optically finished glass or other transparent materials, thebonding temperature may be selected to be below the T_(G) and/or thesoftening temperature of the for the glass other transparent materials,thereby avoiding damage to the optical finish. Depending upon thebonding temperature selected, in some embodiments the application ofoptical and/or protective coatings to the transparent sheets (i.e., thatbecome the windows) may be performed after the bonding of the sheets tothe frames, rather than before bonding. In other embodiments, some ofthe optical and/or protective coatings may be applied to the glasssheets prior to bonding, while other coatings may be applied subsequentto bonding. With regard to pressure parameters, a pressure of 105.5kg/cm² (500 psi) is believed suitable for diffusion bonding Kovar framesand the thin sheet materials previously described.

It will be noted that since the diffusion bonding occurs at hightemperature, the CTE of the glass sheet should be matched to the CTE ofthe metallic frame. To the extent that the CTEs cannot be completelymatched (e.g., due to non-linearities in the CTEs over the range ofexpected temperatures), then it is preferred that the CTE of the glasssheet be lower than the CTE of the metallic frame. This will result inthe metallic frame shrinking more than the glass sheet as the combinedwindow/frame assembly cools from its elevated bonding temperature (orfrom an elevated operational temperature) back to room temperature. Theglass will therefore be subjected primarily to compression stress ratherthan tension, which reduces the tendency for cracking.

Referring now to FIGS. 20 c and 20 d, there is illustrated an additionalembodiment of the invention, a window assembly having internal andexternal frames. FIG. 20 c illustrates the components of window assembly2070 before assembly, while FIG. 20 d illustrates the completedassembly. The window assembly 2070 includes separate frame members 2072and 2074, which are bonded (using diffusion bonding, soldering, brazingor other techniques disclosed herein) to the inner and outer surfaces2076 and 2078, respectively, of the transparent sheet 2080. In otherwords, the transparent window material is “sandwiched” between a layerof frame material on the top of the window and a layer of frame materialon the bottom of the window. Interlayers 2082 and 2084 may be providedfor diffusion bonding as previously described, or alternatively, solderpreforms (also shown as 2082 and 2084) may be provided for bonding bysoldering as previously described.

Typically, the same bonding technique will be used for bonding both theinternal and external frames to the window, however, this is notrequired. Similarly, the internal and external bonds will typically beformed at the same time, however, this in not required. The internalframe 2072 must, however, be hermetically bonded to the window 2080 toproduce a hermetic window assembly. A hermetic bond is not typicallyrequired for bonding the external frame 2074 to the window 2080,however, it may be preferred for a number of reasons.

One benefit of window assemblies having the so-called “sandwiched” frameconfiguration is to equalize the stresses on the internal and externalsurfaces, 2076 and 2078, respectively, of the transparent sheet 2080that are caused by differential thermal expansion characteristics of theframes 2072 and 2074 and sheet (due to unequal CTE), e.g., duringcooling after bonding, or during thermal cycling. Put another way, whena window assembly has a frame bonded to only one surface, unevenexpansion and contraction between the frame and sheet may producesignificant shear stresses within the sheet. These shear stresses may bestrong enough to cause shear failure (e.g., cracking or flaking) withinthe transparent sheet even though the window-to-frame bond itselfremains intact. When a frame is bonded to both the internal and externalsurfaces of the window, however, the shear stresses within the glass (orother transparent material) may be significantly reduced. This isparticularly true if the same material or material having similar CTEsare used for both the internal and external frames. Thisstress-equalization through the thickness of the window increases thereliability and durability of the assembled window during subsequentthermal cycling and/or physical shock.

Sandwiched construction may be used in window assemblies or in WLPassemblies. Sandwiched construction with internal and external frames isespecially advantageous where the sheet and frame materials havesignificantly different CTEs. In addition to the stress balancingfeatures of sandwiched construction, use of an external frame on thesheet may have additional benefits, including: enhancing thermalspreading across the window; enhancing heat dissipation from theassembly; serving as an optical aperture; facilitating thealigning/fixturing or clamping of the device during bonding or assemblyto higher level assemblies; and to display working symbolization.

Referring now to FIGS. 21 a and 21 b, there are illustrated two examplesof hermetically sealed wafer-level packages (also known as “WLPs”) formicro-devices in accordance with other embodiments of the invention.These embodiments are substantially similar to one another, except thatwafer-level package 2002 (FIG. 21 a) has reverse-side externalelectrical connections while wafer-level package 2024 (FIG. 21 b) hassame-side external electrical connections. The wafer-level packages,while similar in many respects to the discrete device packagespreviously disclosed herein, utilize the substrate of the micro-deviceitself, typically a semiconductor substrate, as a portion of thepackage's hermetic envelope. Such wafer-level packaging provides a veryeconomical method for hermetically encapsulating wafer-fabricatedmicro-devices, especially where high production volumes are involved. Aswill be described below, a single micro-device may be packaged using WLPtechnology, or multiple micro-devices on the original production wafermay be packaged simultaneously using WLP technology in accordance withvarious aspects of the current invention.

Referring now specifically to FIG. 21 a, the wafer-level package 2002encloses one or more micro-devices 2004, e.g., a MEMS device or MOEMSdevice fabricated on a substrate 2006. The substrate 2006 is typically awafer of silicon (Si) or gallium arsenide (GaAs) upon which electroniccircuitry 2008 associated with the micro-device 2004 is formed usingknown semiconductor fabrication methods. Electrical vias 2010 (shown inbroken line) may be formed in the substrate 2006 using known methods toconnect the circuitry 2008 to externally accessible connection pads 2012disposed on the reverse side (i.e., with respect to the device) of thesubstrate. It will be appreciated that the path of vias 2010 shown inFIG. 20 has been simplified for purposes of illustration. One end of aframe 2014 made of Kovar or other metallic material is hermeticallybonded to the substrate 2006, and a transparent window 2016 is, in turn,hermetically bonded to the other end of the frame to complete thehermetic envelope sealing the micro-device within the cavity 2018. Theframe-mating surfaces of the substrate 2006 may be prepared ormetallized with one or more metal layers 2020 to facilitate bonding tothe frame, and similarly the frame-mating surfaces of the window 2016may be prepared or metallized with one or more metal layers 2022 for thesame purpose.

Referring now specifically to FIG. 21 b, the wafer-level package 2024 issubstantially identical to the package 2002 previously described, exceptthat in this case the vias 2026 are routed to external connection pads2028 disposed on the same side of the substrate 2006. Obviously, in suchembodiments, the frame 2014 and window 2016 are dimensioned to leaveuncovered a portion of the substrate's upper surface.

Referring now to FIG. 21 c, there is shown an exploded view of a WLP2100 illustrating one possible method of manufacture. To packageindividual or multiple micro-devices using WLP methods, the followingcomponents are necessary: a substrate 2006 having a micro-device 2004thereupon; a frame/spacer 2014 having a continuous sidewall 2015 andthat is “taller” than the device to be encapsulated (to provideclearance); and a transparent sheet or window 2016. Depending upon thebonding method to be used, solder preforms of a metal alloy or glasscomposition, or interlayers for diffusion bonding 2102 and 2103 may alsobe required. It will be appreciated that the top preform 2102 (betweenthe window 2106 and the frame 2014) may be a different material than thebottom preform 2103 (between the frame 2014 and the substrate 2006).

Briefly, the steps for forming the package 2100 are as follows: A firstframe-attachment area 2104 is prepared on the surface of the wafersubstrate 2006 of the subject micro-device. This first frame-attachmentarea 2104 has a plan (i.e., configuration when viewed from above) thatcircumscribes the micro-device or micro-devices 2004 on the substrate2006. A second frame-attachment area 2106 is prepared on the surface ofthe window 2016. The second frame-attachment area 2106 typically has aplan substantially corresponding to the plan of the firstframe-attachment area 2104. The execution order of the previous twosteps is immaterial. Next, the frame/spacer 2014 is positioned betweenthe substrate 2006 and the window 2016. The frame/spacer 2014 has a plansubstantially corresponding to, and in register with, the plans of thefirst and second frame-attachment areas 2104 and 2106, respectively. Ifapplicable, the solder preforms 2102 and 2103 or diffusion bondinginterlayers 2102 and 2103 are interposed at this time between theframe/spacer 2014 and the frame-attachment areas 2104 and/or 2106.Finally, the substrate 2006, frame/spacer 2014 and window 2016 arebonded together (facilitated by solder or glass preforms 2102 and 2103or diffusion bonding interlayers 2102 and 2103, if applicable) to form ahermetically sealed package encapsulating micro-device 2004 within, butallowing light to travel to and/or from the micro-device through thetransparent aperture area 2108 of the window.

It will be understood that diffusion bonding of the package 2100 can beperformed in a single (combined) step or in a number of sub-steps. Forexample, all five components (sheet 2016, first interlayer 2102, frame2014, second interlayer 2103 and substrate 2006) could be stacked in asingle fixture and simultaneously heated and pressed together to causediffusion bonds to form at each of the sealing surfaces. Alternatively,the window sheet 2016 may be first diffusion bonded to the frame 2014using first interlayer 2102 (making a first subassembly), and then thisfirst subassembly may be subsequently diffusion bonded to the substrate2006 using second interlayer 2103. In another alternative, the frame2014 could be diffusion bonded to the substrate 2006 using secondinterlayer 2103, and then the transparent sheet 2016 may subsequently bebonded to the sub-assembly using first interlayer 2102. The choice ofwhich bonding sequence to be used would, of course, depend upon theexact materials to be used, the heat sensitivity of the transparentmaterial in the sheet 2016, the heat sensitivity of the micro device2004 and, perhaps, other parameters such as the expansioncharacteristics of the frame 2014 and interlayer materials.

It will further be appreciated that the current invention is similar inseveral respects to the manufacturing of the “stand-alone” hermeticwindow assemblies previously described. The preparing of theframe-attachment areas 2106 of the window 2016 may be performed usingthe same techniques previously described for use in preparing the sheetseal-ring area 318, including cleaning, roughening, and/or metallizingwith one or more metallic layers as set forth in the earlier Examples1-96.

While the transparent windowpane 2016 may be roughened (e.g., inpreparing the frame-attachment area 2106) to promote adhesion of thefirst metallic layer being deposited onto it (e.g., by CVD or PVD), thewafer substrate 2006 will not typically be roughened in the same manner.Instead, the initial metallic layer on the wafer substrate 2006 willtypically be deposited using conventional wafer fabrication techniques.Where conventional methods of wafer fabrication include the requirementor option of etching a silicon or GaAs wafer to promote adhesion of ametal's deposition, then the same practice may be followed in preparingthe frame attachment area 2104 on the wafer substrate 2006 when buildingWLP devices.

Other wafer or substrate materials include, but are not limited to,glass, diamond and ceramic materials. Some ceramic wafers are known asalumina wafers. These alumina wafers or substrates may be multi-layersubstrates, and may be manufactured using Low-Temperature Co-Fired(LTCC) or High-Temperature Co-Fired (HTCC) materials and processes. LTCCand HTCC substrates often have internal and external electricalcircuitry or interconnections. This circuitry is typically screenprinted onto the ceramic or alumina material layer(s) prior to co-firingthe layers together.

Also, any of the bonding techniques and parameters previously describedfor use on window assemblies may be used to hermetically bond the WLPcomponents to one another, including diffusion bonding/TC bonding withor without the use of interlayers, soldering using a solder preform andsoldering using inkjet-dispensed solders. The primary difference is thatwhen making “stand-alone” window assemblies, only two primary components(namely, the transparent sheet/window 304 and frame 302) are bondedtogether, while when making WLPs, three primary components (namely, thewindow 2016, frame 2014 and substrate 2006) are bonded together(sometimes simultaneously). Of course, when producing WLPs usingsoldering techniques, additional components may be required, for exampleone or more solder preforms 2102 or a quantity of inkjet-dispensedsolder. The solder preforms, if used, may be attached to the top and/orbottom of the frame 2014 as one step in the manufacture of that item.This will simplify the alignment of the three major components of theWLP assembly. It will, of course, be appreciated that thispre-attachment of the solder preforms to the frame is also applicable tothe “stand-alone” window assemblies previously described. One of themethods for attaching solder preforms to the window 2016, frame 2014and/or substrate 2006 is to tack the preform in place using a localizedheat source.

Prior to soldering components together, cleaning the surfaces of thesolder preforms and/or the metallized surfaces of the window 2016, frame2014 and/or substrate 2006 may be necessary to remove surface oxides. Itis desirable to avoid using fluxes during the soldering process toeliminate the need for post-soldering or defluxing. Several surfacepreparation technologies are available to prepare the metal and soldersurfaces for fluxless soldering.

Several other processes may be used for preparing the surfaces of windowassemblies or WLP components for soldering to avoid the need to removefluxes after soldering. A first option is to use what is known in thetrade as a no-clean flux. This type of flux is intended to be left inplace after soldering. A second option is the use of gas plasmatreatments for improving solderability without flux. For example, anon-toxic fluorine-containing gas may be introduced that reacts at thesurface of the solder. This reaction forms a crust on the solder anddissolves upon remelt. The welds and joints formed are equal to orbetter than those formed when using flux. Such plasmas offer benefitsincluding the removal by reduction of oxides and glass to promoteimprovements in solderability and wire bondability. Such treatments havebeen indicated on thick film copper, gold and palladium. Additionalcandidate gases for leaving a clean oxide-free surface include hydrogenand carbon monoxide plasma. Still further candidate gases includehydrogen, argon and freon gas combinations. One version of plasmatreatment is known as Plasma-Assisted Dry Soldering (PADS). The PADSprocess coverts tin oxide (present in fluxless solders when unstablereduced tin oxide reoxidizes upon exposure to air) to oxyfluorides thatpromote wetting. The conversion film breaks up when the solder melts andallows reflow. The film is understood to be stable for more than a weekin air and for more than two weeks when the parts are stored innitrogen.

As in the previously described methods for manufacture of individual andmultiple window assemblies for hermetically packaging discretemicro-devices, the selection of compatible materials for the variouscomponents for the manufacture of WLPs is another aspect of theinvention. For example, each of the primary components (e.g., window,frame/spacer and wafer substrate) of the WLP will preferably haveclosely matched CTEs to insure maximum long-term reliability of thehermetic seal. The frame/spacer 2014 may be formed of either a metallicmaterial or of a non-metallic material. The best CTE match will beachieved by forming the frame/spacer 2014 from the same material aseither the wafer substrate 2006 or the window 2016. However, galliumarsenide (GaAs) and silicon (Si) (i.e., the materials typically used forthe wafer substrate) and most glasses (i.e., the material that istypically used for the window) are relatively brittle, at least incomparison to most metals and metal alloys. These non-metallic materialsare therefore typically not as preferred for forming the frame/spacer2014 as are metals or metal alloys, because the metals and metal alloystypically exhibit better resistance to cracking. In fact, the use of ametal or metal alloy for the frame/spacer 2014 is believed to provideadditional resistance to accidental cracking or breaking of the wafersubstrate 2006, window 2016 and complete WLP 2002 after bonding. When ametallic frame/spacer 2014 is employed, it will preferably be platedwith either gold alone, or with nickel and then gold, sometimes tofacilitate diffusion bonding or soldering, but more often, to provide asurface on the frame/spacer that provides various kinds of protectionbetween the frame/spacer and the atmosphere inside the package. If,however, a non-metallic frame/spacer 2014 is employed, then it might bemetallized to facilitate diffusion bonding or soldering. The metallayers used on the frame/spacer 2014 may be the same as those used onthe windowpane 304 for the manufacture of window assemblies, e.g., thefinal layer might be one of chromium, nickel, tin, tin-bismuth and gold.

In selecting compatible materials for the components of WLPs, it isrecognized that silicon (Si) has a CTE ranging from about 2.6 PPM/° K at293° K to about 4.1 PPM/° K at 1400° K. If it is assumed that theoperating temperatures for micro-devices such as MEMS and MOEMS will bewithin the range from about −55° C. to about +125° C., and that theexpected diffusion bonding or soldering temperatures will be within therange from about +250° C. to about +500° C., it may be interpolated thatsilicon wafers of the type used for WLP substrates will have a CTEwithin the range from about 2.3 PPM/° K to about 2.7 PPM/° K. Onemetallic material believed suitable for use in frame/spacers 2014 thatwill be bonded to silicon (Si) substrates is the alloy known as “LowExpansion 39 Alloy,” developed by Carpenter Specialty Alloys. LowExpansion 39 Alloy is understood to have a composition (weight percent;nominal analysis) as follows: about 0.05% C, about 0.40% Mn, about 0.25%Si, about 39.0% Ni, and the balance Fe. Low Expansion 39 Alloy has a CTEthat is understood to range from about 2.3 PPM/° K over the interval of25° C. to 93° C., to about 2.7 PPM/° K at 149° C., to about 3.2 PPM/° Kat 260° C., and to about 5.8 PPM/° K at 371° C.

Similarly, it is recognized that gallium arsenide (GaAs) of the typeused for WLP wafer substrates has a nominal CTE of about 5.8 PPM/° K.Based on material suppliers' data, Kovar alloy is understood to have aCTE ranging from about 5.86 PPM/° K at 20° C. to about 5.12 PPM/° K at250° C. Thus, Kovar alloy appears to be a good choice for frame/spacers2014 that will be bonded to GaAs substrates. Another material believedsuitable for frame/spacers 2014 that will be bonded to GaAs substratesis the alloy known as Silvar™, developed by Texas Instruments Inc.'sMetallurgical Materials Division, of Attleboro, Mass. It is understoodthat Silvar™ is a derivative of Kovar with CTE characteristics closelymatched to GaAs devices.

With regard to the window/lens for WLPs, it is believed that all of theglasses previously described for use in the manufacture of individualand multiple window assemblies having Kovar frames, e.g., Corning 7052,7050, 7055, 7056, 7058 and 7062, Kimble (Owens Corning) EN-1, KimbleK650 and K704, Abrisa soda-lime glass, Schott 8245 and Ohara CorporationS-LAM60, will be suitable for the window/lens 2016 of WLPs having a GaAssubstrate 2006. Pyrex glasses and similar formulations are believedsuitable for the window/lens 2016 of WLPs having silicon substrates2006. The properties of Pyrex, per the Corning website, are: softeningpoint of about 821° C., annealing point of about 560° C., strain pointof about 510° C., working point of about 1252° C., expansion (0-300° C.)of about 32.5×10⁻⁷/° C., density of about 2.23 g/cm³, Knoop hardness ofabout 418 and refractive index (at 589.3 nm) of about 1.474.

Referring now to FIG. 22, there is illustrated a semiconductor wafer2202 having a plurality of micro-devices 2204 formed thereupon. It willbe appreciated that methods for the production of multiple micro-deviceson a single semiconductor wafer are conventional. Heretofore, however,when the micro-devices 2204 are of the type which must be hermeticallypackaged prior to use, e.g., MEMS, MOEMS, opto-electronic or opticaldevices, it has been standard practice in the industry to first“individuate” or “singulate” the micro-devices, e.g., by cutting-apart,dicing (apart) or breaking-apart the wafer 2202 into sections having,typically, only a single micro-device on each, and then packaging theindividuated micro-devices in separate packages. Now, in accordance withadditional embodiments of the current invention, multiple micro-devicesmay be individually hermetically packaged, or hermetically packaged inmultiples, in a WLP prior to individuation or singulation of thesubstrate wafer. This process is referred to as multiple simultaneouswafer-level packaging, or “MS-WLP.”

Referring now to FIGS. 23 through 29, there is illustrated one methodfor MS-WLP of micro-devices. Briefly, this method includes the steps of:a) preparing a first frame-attachment area on the surface of asemiconductor wafer substrate having a plurality of micro-devices, thefirst frame-attachment area having a plan circumscribing individual (ormultiple) micro-devices on the substrate; b) preparing a secondframe-attachment area on the surface of a window (i.e., a sheet oftransparent material), the second frame-attachment area having a plansubstantially corresponding to the plan of the first frame-attachmentarea; c) positioning a frame/spacer between the substrate and thewindow, the frame/spacer having a plan substantially corresponding to,and in register with the plans of the first and second frame-attachmentareas, respectively; and d) hermetically bonding the substrate,frame/spacer and window together so as to encapsulate the micro-device.If applicable, solder preforms or other materials including, but notlimited to, innerlayers of interlayers for diffusion bonding, are alsopositioned between the frame/spacer and the window and/or substratebefore bonding.

Referring now specifically to FIG. 23, the frame-attachment area 2302 ofsemiconductor wafer 2202 has been prepared by depositing metallizedlayers onto the surface of the wafer substrate completely around (i.e.,circumscribing) each micro-device 2204. In the embodiment shown, theprepared frame-attachment area 2302 includes a rectangular gridconsisting of double-width metallized rows 2304 and columns 2306(interposed between the micro-devices 2204) surrounded by single-widthouter rows 2308 and columns 2310. The composition and thickness of themetallized layers in frame-attachment area 2302 may be any of thosepreviously described for use in preparing the sheet seal-ring area 318as set forth in Examples 1-96.

Referring now to FIG. 24, there is illustrated a MS-WLP frame/spacer2402 for attachment between the wafer 2202 and the window sheet 2602 ofthe MS-WLP assembly. It will be appreciated that in this embodiment, theMS-WLP frame/spacer 2402 has double-width row members 2404 and columnmembers 2406 surrounded by single-width outer row members 2408 andcolumn members 2410, resulting in a plan which corresponds substantiallywith the plan of the frame-attachment area 2302 on the wafer substrate2202. As will be further described below, the purpose of thedouble-width row and column members 2404 and 2406 is to allow room forcutting the frame during singulation of the MS-WLP assembly afterbonding. It will be appreciated that, in other embodiments, the MS-WLPframe/spacer may have a different configuration. In this embodiment, theMS-WLP frame/spacer 2402 is formed of a metal alloy having a CTEsubstantially matched to the CTE of wafer substrate, however, in otherembodiments the frame/spacer may be formed of non-metallic materials aspreviously described. Also as previously described, the frame/spacer2402 will preferably be plated or metallized to facilitate the bondingprocess.

Referring now to FIGS. 25 a-25 d, there are illustrated details of apreferred configuration for the frame/spacer 2402. FIG. 25 a shows anenlarged plan view of a portion of the double-width column member 2406and FIG. 25 b shows an end view of the same portion. It will beappreciated that the row members 2404 of the frame/spacer 2402preferably have a similar configuration. The member 2406 is formed tohave a “groove” 2502, or reduced thickness area, running along thecentral portion of each member, i.e., between the adjacent micro-devicesin the completed MS-WLP assembly. As will be further described below,the groove 2502 facilitates cutting apart of the MS-WLP assembly duringsingulation of the packaged micro-devices. After being cut apart alongthe groove 2502, the frame member 2406 will be divided into twosingle-width members 2504, each one having the configuration shown inFIGS. 25 c and 25 d. During assembly, the grooved side 2505 of the framemember is preferably positioned against the wafer substrate 2202, whilethe ungrooved side 2505 is positioned against the window sheet.

Referring now to FIG. 26, there is illustrated a MS-WLP window sheet2600 for attachment to the MS-WLP frame/spacer 2402. The window sheet2600 is formed of glass or other transparent material having a CTEcompatible with the other principal components of the assembly aspreviously described. At least the inner side (i.e., the side that willbe inside the hermetic envelope) of the sheet 2600, and preferably bothsides, must be optically finished. Any desired optical or protectivecoatings are preferably present on at least the inner side, andpreferably on both sides, of the sheet 2600 at this point. However, ifthe sheet 2600 is attached to only the frame/spacer 2402 in the first oftwo bonding operations, then the optical or protective coatings may beapplied prior to the second, later bonding step of attaching the windowassembly to the wafer. A frame-attachment area 2602 is prepared on theMS-WLP window sheet 2600 so as to circumscribe a plurality of windowapertures 2603 that will ultimately be aligned with the micro-devices2204 in the final MS-WLP assembly. In the embodiment shown, the preparedframe-attachment area 2602 takes the form of metallic layers depositedon the sheet 2600 in a rectangular grid consisting of double-width rows2604 and columns 2606 surrounded by single-width outer rows 2608 andcolumns 2610. This results in a plan for the frame-attachment area 2602that corresponds substantially with the plan of the frame/spacer 2402.The composition and thickness of the metallized layers 2604, 2606, 2608and 2610 in the frame-attachment area 2602 may be any of thosepreviously described for use in preparing the sheet seal-ring area 318of the “stand-alone” windows set forth in Examples 1-96.

In some embodiments, the inner surface of the window sheet 2600 may bescribed, e.g., with a diamond stylus, through each portion of theframe-attachment area 2602 to facilitate breaking apart of the MS-WLPassembly during singulation. The scribing of the window sheet 2600 wouldobviously be performed prior to bonding or joining it to theframe/spacer 2402. Where the frame/spacer 2402 includes grooved memberssuch as those illustrated in FIGS. 25 a-25 b, then the scribe lines onthe sheet 2600 will preferably be in register with the grooves 2502 ofthe frame members in the MS-WLP assembly.

Referring now to FIG. 27, there is illustrated a side view of a completeMS-WLP assembly 2700. It will be appreciated that the proportions ofsome of the components shown in FIG. 27 (e.g., the thicknesses of themetallic layers) may be exaggerated for purposes of illustration. Theframe/spacer 2402 is positioned between the wafer substrate 2202 (withassociated micro-devices 2204) and the window sheet 2600, with the plansof the frame-attachment areas 2302 and 2602 being substantially inregister with the plan of the frame/spacer 2402 such that eachmicro-device or set of micro-devices 2204 is positioned beneath a windowaperture area 2603 of the window sheet. Of course, if the assembly 2700is bonded using solder technology, then solder preforms (not shown)having a plan substantially corresponding with the frame-attachmentareas 2302 and 2602 are also positioned between the frame/spacer 2402and the frame-attachment areas prior to bonding. Also, if innerlayers orinterlayers are used in conjunction with diffusion bonding, theseinterlayers (not shown) having a plan substantially corresponding withthe frame-attachment areas 2302 and 2602 are also positioned between theframe/spacer 2402 and the frame-attachment areas prior to bonding. Anyof the previously described bonding technologies may be used toeffectuate the bond between the components. The MS-WLP assembly 2700will look essentially the same before bonding and after bonding (exceptfor incorporation into the bond area of any solder preforms).

After bonding, the MS-WLP assembly 2700 is cut apart, or singulated, toform a plurality of hermetically sealed packages containing one or moremicro-devices each. There are several options carrying out thesingulation procedure. However, since the window sheet 2600, frame 2402and wafer substrate 2202 are bonded together, simply scribing andbreaking the window sheet (as was done for the multiple stand-alonewindow assemblies) is not practical. Instead, at least the window sheet2600 or the wafer substrate 2202 must be cut. The remaining portion maythen either be cut, or scribed and broken. It is believed that the bestresult will be obtained by cutting the wafer substrate 2202 using awafer-dicing saw, and then either scribing-and-breaking the window sheet2600, or cutting the window sheet using a similar dicing saw.

Referring now to FIG. 28, there is illustrated one option forsingulation of a MS-WLP assembly. The MS-WLP assembly 2800 shown in FIG.28 is similar in most respects to the assembly 2700 shown in FIG. 27,however, in this case the window sheet 2600 was pre-scribed (as denotedby reference number 2802) through the metallic layers 2406, if employed(and also layers 2404 running perpendicular thereto, also if employed)of the interior frame-attachment areas. After bonding, the assembly 2800is cut from the outer side of the wafer substrate 2202 (as indicated byarrow 2804) completely through the substrate and into the groove 2502 ofinterior frame/spacer members 2606 (and also members 2604 runningperpendicular thereto). The cut 2804 does not, however, continue throughthe window sheet 2600. Instead, after the wafer substrate 2202 and frame2402 are cut, the window sheet 2600 is broken by bending it along thepre-scribed lines 2802. The assembly 2800 may be first broken into rows,then each row broken into individual packages along the column lines, orvice versa. In one variation of this method, the window sheet 2600 isnot pre-scribed, but instead is scribed through the kerf 2806 formed bycutting through the wafer substrate 2202 and frame 2402. It will beappreciated that this scribing must be sufficiently forceful to cutthrough the remaining portion of the frame member 2406 and metalliclayers 2606 under the groove 2502. The assembly is then broken intoindividual packages along the scribe lines as before.

Referring now to FIG. 29, in another variation, a MS-WLP assembly 2900is individuated by simply cutting completely through the wafer substrate2202, frame/spacer 2402 and window sheet 2600 between each micro-device2204 as indicated by arrow 2902. The result is a plurality ofindividually WLP micro-devices 2904. The individuating cuts may be madefrom either the window side or the substrate side, however, it may benecessary to protect the outer surface of the window sheet (e.g., withmasking tape, etc.) to protect it from damage during the sawingoperation.

When electrical-resistance heating (“ERH”) is used to facilitatediffusion bonding or soldering of the components of a MS-WLP assembly,the electrical current is typically applied so that it flows throughboth the window/frame junction and the frame/substrate junctionsimultaneously. To facilitate this ERH heating, the configuration of theMS-WLP assembly may be modified to provide “sacrificial” metallizedareas (i.e., areas that will be discarded later) on the window sheet andwafer substrate for placement of ERH electrodes. Preferably, theelectrode placement areas on the substrate and window will be accessiblefrom directions substantially perpendicular to the wafer.

Referring now to FIG. 30, there is illustrated a wafer 3000 similar inmost respects to the wafer 2002 of FIG. 23, i.e., having a plurality ofmicro-devices 2204 formed thereon and a metallized frame-attachment area3002 formed thereon so as to surround the micro-devices. In this case,however, the wafer 3000 further includes a metallized electrodeplacement pad 3004 positioned at one end of the wafer. The electrodeplacement pad 3004 is in electrical contact with the metallized layers2304, 2306, 2308 and 2310 of the frame-attachment area 3002.

Referring now to FIG. 31, there is illustrated window sheet 3100 similarin most respects to the sheet 2600 of FIG. 26, i.e., having a metallizedframe-attachment area 3102 formed thereon so as to surround the windowaperture areas 2603 on the sheet. In this case, however, the sheet 3100further includes a metallized electrode placement pad 3104 positioned atone end of the sheet. The electrode placement pad 3104 is in electricalcontact with the metallized layers 2604, 2606, 2608 and 2610 of theframe-attachment area 3102.

Referring now to FIG. 32, there is illustrated a MS-WLP assembly 3200 inaccordance with another embodiment. The components of the assembly 3200are positioned such that the wafer substrate 3000 and the window sheet3100 are adjacent to the frame/spacer 2402, but the respectivemetallized electrode placement pads 3004 and 3104 overhang on oppositesides of the assembly. This configuration provides unobstructed accessto the pads 3004 and 3104 in a direction perpendicular to the wafer (asdenoted by arrows 3202), allowing easy attachment of electrodes for ERHprocedures.

During bonding of WLP assemblies, there are two bonds that shouldtypically occur simultaneously: the junction between the frame/spacerand the window sheet and the junction between the frame/spacer and thewafer substrate. As was described previously, however, the window mayfirst be bonded only to the frame, and later, using ERH, thewindow/frame assembly can be attached to the substrate of the device. Aswas previously described in the process for the manufacturing ofstand-alone window assemblies, the configuration of the metal frame andplacement of ERH electrodes may be critical for even heating using ERHheating techniques. Similarly, for MS-WLP devices, the metallizationpatterns and ERH electrode placement locations on the wafer substrateand the window sheet may be important to achieving even heating.Therefore, the size/shape of the frame including possibly excess orsacrificial features, and the metallization patterns on both the windowsheet and the wafer substrate should be concurrently designed, modeled(e.g., using software simulation) and prototyped to ensure even heatingof the bonded surfaces/features.

It will be appreciated that the previous embodiment describes a methodfor manufacturing MS-WLP assemblies which is suited for micro-deviceshaving opposite-side electrical connection pads. Referring now to FIG.33, there is illustrated a micro-device having same-side electricalconnections. The micro-device 3300 is disposed on one side of asemiconductor substrate 3302. A plurality of vias 3304 run from theactive areas of the micro-device, through the substrate, and to aplurality of connection pads 3306 located on the same side of thesubstrate. Obviously, the electrical connection pads 3306 must beaccessible even after the micro-device 3300 has been sealed within itshermetic package. In the following embodiment, there is presentedanother method for manufacturing MS-WLP assemblies suited for use withsuch micro-devices with same-side connections.

Referring now to FIG. 34, there is illustrated a wafer 3402 having aplurality of micro-devices 3300 formed thereupon, each micro-devicehaving one or more sets 3403 of associated same-side connection pads3306. In accordance with this embodiment, the multiple micro-devices3300 are individually hermetically packaged in a WLP prior toindividuation of the substrate wafer 3402, however the same-sideelectrical connection pads 3306 remain accessible. The steps of thisembodiment are similar in many respects to those of the previousembodiment, except for the changes described below.

Referring now to FIG. 35, the frame-attachment area 3502 of thesemiconductor wafer 3402 is first prepared, in this case by depositingmetallized layers onto the surface of the wafer substrate circumscribingeach micro-device 3300. In the embodiment shown, the preparedframe-attachment area 3502 includes three “ladder-shaped” grids 3503,each consisting of double-width metallized rows 3504 (i.e., the “rungs”of the ladder) and single-width columns 3506 (the “sides” of the ladder)connected by buss strips 3508 at each end. The composition and thicknessof the metallized layers in frame-attachment area 3502 may be any ofthose previously described for use in preparing the sheet seal-ring areaor frame attachment areas.

Referring now to FIG. 36, there is illustrated a MS-WLP frame/spacer3602 for attachment between the wafer 3402 and the window sheet 3702(FIG. 37) of the MS-WLP assembly. It will be appreciated that in thisembodiment, the MS-WLP frame/spacer 3602 is configured into multipleladder shaped portions 3603, each portion having double-width rungmembers 3604 and single-width side members 3606 that are configured tohave a plan substantially corresponding to the ladder-shaped plans 3503of the frame-attachment area 3502 on the wafer substrate 3402. Theladder-shaped portions 3603 are attached to, and held in relativeposition to one-another by, connecting members 3608 located at oppositeends of the frame/spacer 3602. As in the previous embodiment, thedouble-width members 3604 allow room for cutting the frame 3602 betweenmicro-devices during singulation of the MS-WLP assembly (i.e., afterbonding). In a preferred embodiment, the double-width members may have agrooved cross-section (e.g., similar to that shown in FIGS. 25 a and 25b) to facilitate their cutting apart. It will be appreciated however,that in other embodiments the MS-WLP frame/spacer may have a differentconfiguration. In this embodiment, the MS-WLP frame/spacer 3602 isformed of a metal alloy having a CTE substantially matched to the CTE ofthe wafer substrate, however, in other embodiments the frame/spacer maybe formed of non-metallic materials as previously described. Also aspreviously described, the frame/spacer 3602 will preferably be plated ormetallized to facilitate the subsequent bonding process.

Referring now to FIG. 37, there is illustrated a MS-WLP window sheet3700 for attachment to the MS-WLP frame/spacer 3602. The window sheet3700 is formed of glass or other transparent material having a CTEcompatible with the other principal components of the assembly aspreviously described. At least the inner side (i.e., the side that willbe inside the hermetic envelope) of the sheet 3700 (and preferably bothsides) is optically finished, and any desired optical or protectivecoatings are in place on the inner side. Either before or after anydesired optical or protective coatings are in place on the inner side ofsheet 3700 (and preferably both sides), a frame-attachment area 3702 isprepared on the MS-WLP window sheet 3700 so as to circumscribe aplurality of window apertures 3705 that will ultimately be aligned withthe micro-devices 3300 in the final MS-WLP assembly. In the embodimentshown, the prepared frame-attachment area 3702 includes metallic layersdeposited on the sheet 3700 in multiple ladder-shaped portions 3703,each portion including double-width rung members 3704 and single-widthside members 3706. Each ladder portion 3703 has a plan that correspondssubstantially with the plan of the ladder portions 3603 of theframe/spacer 3602. The methods and procedures for preparation of thewindow sheet 3700, including the composition and thickness of themetallized layers 3704 and 3706 in the frame-attachment area 3702, maybe any of those previously described for use in preparing the sheetseal-ring area 318 of the “stand-alone” window assemblies or the frameattachment areas 2602 of the window sheet 2600 of the MS-WLP.

In the embodiment illustrated in FIG. 37, the metallized layers ofwindow sheet 3700 extend beyond the ladder-shaped portions 3703, andincluded additional portions configured to facilitate electricresistance heating (ERH). These additional portions include electrodeattachment portions 3708 and bridge portions 3710, both of which areelectrically connected to the metallized layers 3704 and 3706 of theladder portions 3703. The configuration, e.g., placement and thickness,of these electrode attachment portions 3708 and bridge portions 3710 areselected to manage the flow of ERH current through the interfacesbetween the metallized portions of the window sheet 3700 and theframe/spacer 3602, and through the interface between the frame/spacer3602 and the metallized portions of the substrate 3402, therebycontrolling the heating at these interfaces during ERH-facilitatedbonding operations.

As in previous embodiments, the inner surface of the window sheet 3700may be scribed, e.g., with a laser or diamond stylus, through eachportion of the frame-attachment area 3702 to facilitate breaking apartof the MS-WLP assembly during singulation. Where the frame/spacer 3602includes grooved members such as those illustrated in FIGS. 25 a-25 b,then the scribe lines on the window sheet 3700 will preferably be inregister with the grooves 2502 of the frame members in the MS-WLPassembly.

Referring now to FIG. 38, there is illustrated a top view of a completeMS-WLP assembly 3800 including the wafer substrate 3402, frame/spacer3602 and window sheet 3700 stacked on one another such that theladder-shaped areas 3503, 3603 and 3703 of each respective component aresubstantially in register with one another, and such that each of themicro-devices 3300 is positioned beneath a window aperture area 3705 ofthe window sheet. It will be appreciated that in this embodiment, theconfigurations of the wafer 3402 and window sheet 3700 are complementaryto facilitate the placement of ERH electrodes. Specifically, theportions of the wafer 3402 having the metallized buss strips 3508project past the edges of the sheet 3700 (when viewed from above),allowing one set of ERH electrodes to make contact from verticallyabove, while the portions of the sheet having the metallized contactportions 3708 project past the edge of the wafer (when viewed frombelow), allowing another set of ERH electrodes to make contact fromvertically below.

Of course, if the assembly 3800 is to be bonded using solder technology,then solder preforms (not shown) having a plan substantiallycorresponding with the frame-attachment areas are also positionedbetween the frame/spacer 3602 and the frame-attachment areas of thewindow sheet 3700 and substrate 3402 prior to bonding. Any of thepreviously described bonding technologies may be used to effectuate thebond between the components. If the assembly 3800 is to be bonded usingdiffusion bonding technology, then when using interlayer preforms (notshown), these preforms will have a plan substantially corresponding withthe frame-attachment areas and are also positioned between theframe/spacer, 3602 and the frame-attachment areas of the window sheet3700 and/or between the frame/spacer 3602 and substrate 3402 prior tobonding. The MS-WLP assembly 3800 will look essentially the same beforebonding and after bonding (except for incorporation into the bond areaof any solder preforms or interlayers for diffusion bonding).

After bonding, the window sheet 3700 of the assembly 3800 may be viewedas including primary strip portions 3802, which overlie the plurality ofencapsulated micro-devices 3300, secondary strip portions 3804, whichare interposed between the primary strips and overlie rows ofnon-encapsulated contact pads 3403, and end strip portions 3806, whichare disposed at each end of the window sheet and also overlie rows ofnon-encapsulated contact pads 3403. During singulation of the assembly3800, the secondary and end strip portions 3804 and 3806, respectively,of the window sheet are cut away and discarded, these parts beingessentially “sacrificial.” Further during singulation, the substrate3402 is divided along cut lines (denoted by arrows 3808) between thecolumns of micro-devices 3300 and contact pads 3403 to form multi-unitstrips. The separating of the window sheet may be performed using saws,lasers or other conventional means, while the dividing of the substratemay be performed using saws, lasers, or by snapping along a score line.

Referring now to FIGS. 39 and 40, singulation of the MS-WLP assembly3800 is illustrated. Referring first to FIG. 39, there is illustrated amulti-unit strip 3900 which has been separated from the MS-WLP assembly3800. The multi-unit strip 3900 includes a plurality of micro-devices3300 on a portion 3902 of the original wafer substrate 3402, themicro-devices being encapsulated within adjacent hermetic envelopeshaving one or more micro-devices under each window portion 3705 of theoriginal window sheet, but with their associated electrical contact pads3403 being non-encapsulated. The multi-unit strip 3900 is further cutapart, or singulated, along cut lines 3904, which in this embodimentcorresponds to the center of the frame members 3604 separating theadjacent hermetic envelopes. The result is a plurality of discretehermetically sealed WLP packages containing one or more micro-devicesunder each window portion 3705. An example of an individual WLP package4000 produced by this method is illustrated in FIG. 40.

During the singulation of multi-unit strips 3900, at least the windowsheet 3700 or the wafer substrate portion 3902 must be cut. Theremaining portion may then either be cut, or scribed and broken. It isbelieved that the best result will be obtained by cutting the wafersubstrate portion 3902 using a wafer-dicing saw, and then eitherscribing-and-breaking the window sheet 3700, or cutting the window sheetusing a similar dicing saw.

While the invention has been shown or described in a variety of itsforms, it should be apparent to those skilled in the art that it is notlimited to these embodiments, but is susceptible to various changeswithout departing from the scope of the invention.

1. A method for manufacturing a hermetically sealed micro-device packageencapsulating a micro-device and including a transparent portion, themethod comprising the following steps: preparing, on a semiconductorsubstrate having a micro-device operably disposed thereupon, a firstframe-attachment area; preparing, on a sheet of transparent material, asecond frame-attachment area; positioning, between the semiconductorsubstrate and the transparent sheet, a separate frame/spacer that isformed independently from both the semiconductor substrate and the sheetof transparent material, the frame/spacer including a sidewall havingone side substantially in register with the first frame-attachment areaand having the opposite side substantially in register with the secondframe-attachment area; and bonding the substrate, frame/spacer andtransparent sheet together to form a hermetically sealed packageencapsulating the micro-device in a cavity below the sheet.
 2. A methodin accordance with claim 1, wherein the semiconductor substrate issubstantially formed of a material selected from one of silicon (Si) andgallium arsenide (GaAs).
 3. A method in accordance with claim 1, whereinthe step of preparing the first frame-attachment area comprisesdepositing metallic layers onto the semiconductor substrate.
 4. A methodin accordance with claim 1, wherein during the step of bonding, thetemperature of the window aperture portion of the sheet remains belowthe glass transition temperature (T_(G)) of the transparent material. 5.A method in accordance with claim 1, wherein the step of preparing thesecond frame-attachment area comprises depositing metallic layers ontothe transparent sheet.
 6. A method in accordance with claim 1, whereinthe step of bonding further comprises: forming a bond between theframe/spacer and the semiconductor substrate; forming another bondbetween the frame/spacer and the transparent sheet; and wherein at leastone of the bonds is formed by soldering.
 7. A method in accordance withclaim 6, wherein the step of soldering is performed using a solderformed of a material selected from one of a metal alloy and a solderglass.
 8. A method in accordance with claim 1, wherein the step ofbonding further comprises: forming a bond between the frame/spacer andthe semiconductor substrate; forming another bond between theframe/spacer and the transparent sheet; and wherein at least one of thebonds is formed by diffusion bonding.
 9. A method for manufacturing ahermetically sealed micro-device package encapsulating a micro-deviceand including a transparent portion, the method comprising the followingsteps: preparing on a semiconductor substrate having a micro-deviceoperably disposed thereupon, a first frame-attachment area; preparing ona sheet of transparent material, a second frame-attachment area;positioning, between the semiconductor substrate and the transparentsheet, a frame/spacer including a sidewall having one side substantiallyin register with the first frame-attachment area and having the oppositeside substantially in register with the second frame-attachment area;and bonding the substrate, frame/spacer and transparent sheet togetherto form a hermetically sealed package encapsulating the micro-device ina cavity below the sheet; wherein the step of bonding further comprisespressing the substrate and the sheet against the frame/spacer withsufficient force to produce a first predetermined contact pressure alonga first junction region between the frame/spacer and the firstframe-attachment area of the substrate and a second predeterminedcontact pressure along a second junction region between the frame/spacerand the second frame-attachment area of the sheet; heating the firstjunction region to produce a first predetermined temperature along thefirst junction region; heating the second junction region to produce asecond predetermined temperature along the second junction region;maintaining the first predetermined contact pressure and the firstpredetermined temperature until a diffusion bond is formed between theframe/spacer and the substrate along the first junction region; andmaintaining the second predetermined contact pressure and the secondpredetermined temperature until a diffusion bond is formed between theframe/spacer and sheet along the second junction region.
 10. A methodfor simultaneously manufacturing multiple sealed micro-device packages,each package encapsulating at least one micro-device and including atransparent portion, the method comprising the following steps:preparing, on a semiconductor substrate having a plurality ofmicro-devices disposed thereupon, a first frame-attachment area thatcircumscribes a number of the micro-devices; preparing, on a sheet oftransparent material, a second frame-attachment area; positioning,between the semiconductor substrate and the transparent sheet, aseparate frame/spacer that is formed independently from both thesemiconductor substrate and the sheet of transparent material, theframe/spacer including a plurality of sidewalls, the sidewallscollectively having one side substantially in register with the firstframe-attachment area and an opposite side substantially in registerwith the second frame-attachment area; bonding the semiconductorsubstrate, frame/spacer and transparent sheet together to form amulti-package assembly having a plurality of sealed cavities separatedfrom one another by the frame/spacer sidewalls, each of the cavitiescontaining at least one of the micro-devices positioned below the sheet;and dividing the multi-package assembly into individual packages byparting completely through the substrate, frame/spacer sidewall andtransparent sheet at locations between adjacent cavities; whereby eachindividual package will encapsulate at least one of the micro-devices ina sealed cavity.
 11. A method in accordance with claim 10, wherein thesemiconductor substrate is substantially formed of a material selectedfrom one of silicon (Si) and gallium arsenide (GaAs).
 12. A method inaccordance with claim 10, wherein during the step of bonding, thetemperature of the window aperture portions of the transparent sheetremains below the glass transition temperature (T_(G)) of thetransparent material.
 13. A method in accordance with claim 10, whereinthe step of preparing the first frame-attachment area comprisesdepositing metallic layers onto the semiconductor substrate.
 14. Amethod in accordance with claim 10, wherein the step of preparing thesecond frame-attachment area comprises depositing metallic layers ontothe transparent sheet.
 15. A method in accordance with claim 10, whereinthe step of bonding further comprises: forming a bond between theframe/spacer and the semiconductor substrate; forming another bondbetween the frame/spacer and the transparent sheet; and wherein at leastone of the bonds is formed by soldering.
 16. A method in accordance withclaim 15, wherein the step of soldering is performed using a solderformed of a material selected from one of a metal alloy and a solderglass.
 17. A method in accordance with claim 10, wherein the step ofbonding further comprises: forming a bond between the frame/spacer andthe semiconductor substrate; forming another bond between theframe/spacer and the transparent sheet; and wherein at least one of thebonds is formed by diffusion bonding.
 18. A method for simultaneouslymanufacturing multiple sealed micro-device packages, each packageencapsulating at least one micro-device and including a transparentportion, the method comprising the following steps: preparing, on asemiconductor substrate having a plurality of micro-devices disposedthereupon, a first frame-attachment area that circumscribes a number ofthe micro-devices; preparing, on a sheet of transparent material, asecond frame-attachment area; positioning, between the semiconductorsubstrate and the transparent sheet, a frame/spacer including aplurality of sidewalls the sidewalls, collectively having one sidesubstantially in register with the first frame-attachment area and anopposite side substantially in register with the second frame-attachmentarea; bonding the semiconductor substrate, frame/spacer and transparentsheet together to form a multi-package assembly having a plurality ofsealed cavities separated from one another by the frame/spacersidewalls, each of the cavities containing at least one of themicro-devices positioned below the sheet; and dividing the multi-packageassembly into individual packages by parting completely through thesubstrate, frame/spacer sidewall and transparent sheet at locationsbetween adjacent cavities; whereby each individual package willencapsulate at least one of the micro-devices in a sealed cavity whereinthe step of bonding further comprises pressing the substrate and thesheet against the frame/spacer with sufficient force to produce a firstpredetermined contact pressure along a first junction region between theframe/spacer and the first frame-attachment area of the substrate and asecond predetermined contact pressure along a second junction regionbetween the frame/spacer and the second frame-attachment area of thesheet; heating the first junction region to produce a firstpredetermined temperature along the first junction region; heating thesecond junction region to produce a second predetermined temperaturealong the second junction region; maintaining the first predeterminedcontact pressure and the first predetermined temperature until adiffusion bond is formed between the frame/spacer and the substratealong the first junction region; and maintaining the secondpredetermined contact pressure and the second predetermined temperatureuntil a diffusion bond is formed between the frame/spacer and sheetalong the second junction region.
 19. A method for simultaneouslymanufacturing multiple sealed micro-device packages directly on anundiced semiconductor production wafer, each package encapsulating atleast one micro-device and including a transparent window, the methodcomprising the following steps: preparing, on an undiced semiconductorproduction wafer having a plurality of micro-devices disposed thereupon,a first frame-attachment area that circumscribes a number of themicro-devices; preparing, on a sheet of transparent material, a secondframe-attachment area; positioning, between the wafer and thetransparent sheet, a separate frame/spacer that is formed independentlyfrom both the semiconductor substrate and the sheet of transparentmaterial, the frame/spacer including a plurality of sidewalls, thesidewalls collectively having one side substantially in register withthe first frame-attachment area and an opposite side substantially inregister with the second frame-attachment area; bonding the wafer,frame/spacer and transparent sheet together to form a multi-packageassembly having a plurality of sealed cavities separated from oneanother by the frame/spacer sidewalls, each of the cavities containingat least one of the micro-devices positioned below the sheet; anddividing the multi-package assembly into individual packages by partingcompletely through the wafer, frame/spacer sidewall and transparentsheet at locations between adjacent cavities; whereby each individualpackage will encapsulate at least one of the micro-devices in a sealedcavity.
 20. A method in accordance with claim 19, wherein the wafer issubstantially formed of a material selected from one of silicon (Si) andgallium arsenide (GaAs).